Members of the Chicago Teachers Union staffed informational picket lines at six elementary schools on Monday, threatening to strike if a deal on a new contract is not reached by Labor Day, NBCChicago.com reports.

Teachers staged the protests at schools already in session to call attention to stalled contract negotiations, according to NBCChicago.com.

“Students come first, but you can’t have a quality school district by putting a fair and equitable labor agreement last," said Chicago Teachers Union President Karen Lewis in a statement. "After Labor Day we want to be where we belong — in the classroom. However, if talks continue as they have been, we will be where we need to be (and that is) on the line.”

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Union officials have begun printing strike signs, The Associated Press reported on Monday. Upwards of 400,000 students would be affected by a walkout.

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Teachers and school officials have been locked in contract talks since last year and still disagree on wages, health benefits and job security. The Chicago Teachers Union represents 25,000 members.

The union and Board of Education already agreed on one big issue — hiring more teachers to help the district manage a longer school day rather than asking existing teachers to work more hours.

Chicago’s public school students have the shortest school day — 5 hours and 45 minutes — among the nation's 50 largest districts, according the National Council on Teacher Quality. The national average is 6.7 hours in school.

Chicago pushes longer school days as key to achievement

Leaders of the Chicago Public Schools hope more time in the classroom will mean better grades and more high school graduates from the nation's third-largest school system.

"Our focus should be on our kids and reaching a fair agreement at the negotiation table, where we have made significant progress over the last few weeks,” CPS spokeswoman Becky Carroll told NBCChicago.com. “Students must always come first and shouldn't be distracted from their learning especially now that kids throughout the district are benefiting from the start of the full school day." 

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