Andrew Kelly / Reuters

Mark Massey, center, and Dale Frost, right, pose for a picture after registering their marriage at the City Clerk's Office in New York on Oct. 11. New York is one of six states where same-sex marriage is legal.

Updated at 4:34 p.m. ET: A federal appeals court in New York on Thursday became the second appeals court to strike down the Defense of Marriage Act, ruling that the law defining marriage as a union between a man and a woman is unconstitutional.

The 2nd U.S. Circuit Court of Appeals joins the 1st Circuit court in Boston, which handed down its ruling in May, in rejecting a key part of the law. The 2nd Circuit upheld a lower court ruling that DOMA unconstitutionally denies federal benefits to lawfully married same-sex couples.

The constitutionality of same-sex marriage could ultimately be decided by the U.S. Supreme Court, which may take up the issue in its current term.

"Homosexuals are not in a position to adequately protect themselves from the discriminatory wishes of the majoritarian public," Chief Judge Dennis Jacobs wrote for the 2-1 majority. 

"Even if preserving tradition were in itself an important goal, DOMA is not a means to achieve it," he said.

Judge Chester Straub dissented, arguing that the federal definition of marriage should be left to the political process. "If this understanding is to be changed, I believe it is for the American people to do so," he wrote.

Appeals in several DOMA cases are pending before the Supreme Court.

"Next stop, Supreme Court," said Rick Jacobs, founder of the Courage Campaign, a California-based progressive advocacy organization. "Politicians and judges have no business telling anyone who they can love and who they can marry."

The appellate panel ruled in favor of Edith "Edie" Windsor, an 83-year-old lesbian whose partner, whom she married in Canada, died in 2009. Windsor argued that the 1996 law discriminates against gay couples in violation of the Constitution.

Six states have legalized same-sex marriage, including New York in 2011. Because of the Defense of Marriage Act, federal law and government programs do not recognize those marriages. 

Read the appeals court opinion (PDF)

Windsor had to pay $363,000 in federal taxes after inheriting property from Thea Spyer, to whom she was married. The IRS stated the marriage was not recognized at the federal level and imposed the estate tax.

"Given her age and health, we are eager for Ms. Windsor to get a refund of the unconstitutional tax she was forced to pay as soon as possible," Roberta Kaplan, her legal counsel, said in a statement.

"This law violated the fundamental American principle of fairness that we all cherish," added Windsor. "I know Thea would have been so proud to see how far we have come in our fight to be treated with dignity."

Shannon Stapleton / Reuters

Edith Windsor speaks to reporters after a hearing before the appeals court on Sept. 27.

The Obama administration said last year it considered DOMA unconstitutional and would no longer defend it. Instead, a group appointed by the Republican majority in the U.S. House of Representatives is defending the law in courts across the country.

The appeals court rejected the group's arguments that the law was necessary to maintain a uniform definition of marriage, that it served the government's interest of saving money and that it was necessary to encourage procreation.

Referring to the House Republican leadership, which is defending the law in court because it holds a 3-2 majority on the House's Bipartisan Legal Advisory Group, Jacobs wrote:

BLAG argues that, unlike protected classes, homosexuals have not "suffered discrimination for longer than history has been recorded." But whether such discrimination existed in Babylon is neither here nor there. BLAG concedes that homosexuals have endured discrimination in this country since at least the 1920s. Ninety years of discrimination is entirely sufficient to document a "history of discrimination."

Jacobs was appointed in 1992 by by President George H. W. Bush to serve on the Second Circuit. He was joined in his opinion by Judge Christopher Droney, an Obama appointee. Straub, who wrote the dissent, is a Clinton appointee.

The decision came less than a month after the court heard arguments on Sept. 27.   

Lawyer Paul Clement, who had argued in support of the law on behalf of the Bipartisan Legal Advisory Group of the House of Representatives, was traveling and did not immediately return a message for comment to The Associated Press.   

James Esseks, an attorney for the American Civil Liberties Union, called the ruling "a watershed moment in the legal movement for lesbian and gay rights."   

"It's fabulous news for same-sex couples in New York and other states," he said.   

Esseks said the 2nd Circuit went farther than the appeals court in Boston by saying that when the government discriminates against gay people, the courts will presume that the discrimination is unconstitutional.   

In striking down the law, Jacobs wrote that the law's "classification of same-sex spouses was not substantially related to an important government interest" and thus violated the equal protection clause of the Constitution.

New York Gov. Andrew Cuomo praised the decision:

"In June 2011, New York State inspired the rest of the nation by becoming the largest state to achieve marriage equality. Today’s ruling by the United States Court of Appeals for the Second Circuit provides further momentum for national progress on this important civil rights issue. What we did here in New York can only be the beginning, and we must continue to work together until all Americans are free to marry whom they love and are entitled to all of the rights and benefits of marriage equally, regardless of sexual orientation."

New York Mayor Michael Bloomberg, who has donated $250,000 to support same-sex marriage backers in Maryland, added:

“Today’s decision affirms that DOMA deprives same sex couples of equal protection under the law. This ruling is an important step in ensuring the rights of men and women are not dependent upon who they love and who they chose to spend their lives with. We have much more to do, but we are another step further on the road to a more perfect union for all Americans.”

The National Organization for Marriage, which opposes same-sex marriage, said it looked forward to a Supreme Court ruling:

“This is yet another example of judicial activism and elite judges imposing their views on the American people, and further demonstrates why it is imperative for the U.S. Supreme Court to grant review in the currently pending DOMA cases as well as to the Proposition 8 case. The American people are entitled to a definitive ruling in support of marriage as the union of one man and one woman, as 32 states have determined through popular vote."

Reuters and The Associated Press contributed to this report.

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Courtesy of GLAAD

Jennifer Tyrrell, right, addresses the media with her partner, Alicia, after delivering a petition to the Boy Scouts of America in Dallas, Tex., on Wednesday in which she calls for an end to the private group's policy banning gay Scouts and leaders.

A woman who was ousted as the head of her son’s Tiger Cubs pack because she is a lesbian on Wednesday delivered a petition with more than 300,000 signatures to the Boy Scouts urging them to end their longstanding policy banning gay Scouts and leaders, saying the organization’s recent decision to stick with the controversial membership standards will not end her campaign.

Jennifer Tyrrell, a 32-year-old, stay-at-home mother of four, was removed from her post as den master in April because she is a lesbian. She has been fighting since then to get the Boy Scouts to change its longstanding policy, starting an online petition calling for the change.

But on Tuesday, the private organization said it was keeping the ban on open or avowed homosexuals.

"I feel like this isn’t going to deter me because I truly love Scouts and I truly ... want to see this change take place, and not just for myself, but for families and children everywhere who have flooded me with emails thanking me for having the courage to stand up because they actually, you know, couldn’t," she told NBC News just after handing over the petition and meeting with two Boy Scouts representatives at the private group's headquarters in Texas.

The three large boxes that Tyrrell gave to the group also contained comments from current and former Scouts and leaders who support ending the policy. Wearing her den master uniform, she was joined by two of her children and her partner, Alicia Burns.

The purpose of the meeting was not to discuss changing the policy, BSA spokesman Deron Smith said in an email to NBC News, but to listen and to receive the petition.

“The Boy Scouts of America works to treats everyone with courtesy and respect," he said. "The discussion was mutually cordial and very respectful. The BSA values the freedom of everyone to express their opinion and believes to disagree does not mean to disrespect.”

Tyrrell said the representatives were polite and professional during the 10-minute meeting, but that "they don't see any change in the future" on the policy. She said they were adamant that the right decision had been made in deciding to maintain the policy after a recent confidential review of it, but also said they were saddened by what happened to her though it was in line with their membership standards.

"It was a very respectful meeting. I think it was productive. I think ... we were both willing to listen," she said, but "we disagree still."

Two of Jennifer Tyrrell's children and her partner, Alicia, wait while Tyrrell speaks to the media after delivering more than 300,000 signatures to the Boy Scouts of America at the group's headquarters in Dallas, Tex., on Wednesday.

She said she told them, "'Well, I guess I’ll see you in the future because we’re going to keep on meeting until we win.”

The Boy Scouts said Tuesday that it began a confidential review of the policy in 2010, convening a diverse committee of 11 senior volunteers and professional leaders to review the membership standards after a resolution was put forward to reconsider them. The committee reached a "unanimous consensus" that it was the "best policy" for the BSA, Smith said. That conclusion was shared at a February board meeting and recently reviewed by the officers of the board.

“The vast majority of the parents of youth we serve value their right to address issues of same-sex orientation within their family, with spiritual advisers, and at the appropriate time and in the right setting,” Bob Mazzuca, chief scout executive of the Boy Scouts, said in a statement. “While a majority of our membership agrees with our policy, we fully understand that no single policy will accommodate the many diverse views among our membership or society.”

The review was conducted confidentially "to allow the committee to make the best decision for the organization," Smith said.

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Tyrrell said she asked the Boy Scouts if they could provide documentation about the review, but her request was declined.

“I would actually like a little bit of proof backing up what they say,” she said before the meeting. “They think that all the Scout parents feel that this is a bad move, they don’t want to change the policy. They’ve never provided any proof saying that. I have proof. I have over 316,000 signatures on a petition,” plus comments from many “relaying the message this is why we want to see this policy changed.”

“The discrimination with adults is bad enough, but you can’t be a gay Scout, either, so that’s … [a] dangerous message that you’re sending the kids, that they are not good enough, that they’re not accepted,” she added. “It’s just not fair to treat children that way and it’s not fair to tell parents that you can’t be involved in your child’s life. So, we’re not going to stop until every parent can participate in Scouts with their child.”

In June, the Boy Scouts said it was considering another resolution proposed at the group's annual meeting the month before that also called for ending the policy. But the decision announced Tuesday means the Scouts’ board will take no more action on that resolution and had no plans to further review the issue, Smith said.

The Boy Scouts’ policy became a focus of the U.S. Supreme Court in 2000, when the justices sided with the organization in a lawsuit involving a former assistant Scoutmaster who was gay, citing the protections of the First Amendment.

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A gay woman who was tossed out as a Cub Scout leader is getting support from other parents.

Jennifer Tyrrell says she was the den leader for Pack 109's Tiger Scouts in Bridgeport, Ohio, for a year before her orientation became an issue.

The Boy Scouts of America has a strict policy when it comes to sexual orientation and membership. "We do not grant membership to individuals who are opened or avowed homosexuals," Bob Drury, the Scouts' executive for the Ohio River Valley, told NBC station WTOV.

But parent Rob Donn said Tyrrell's sexual orientation "was never an issue."

Get more on the story in the video above.

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