This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.CHICAGO —Tuesday was the first day for Chicago Public Schools, but a potential teachers strike could bring classes to a halt this year. CPS teachers are going back to school without a contract in place, but the teachers union said they’re hard at work negotiating a new one. About 360,000 students are headed back to the classroom Tuesday morning, as Chicago Public Schools confront budget cuts and slashed staffing for the new school year. Contract negotiations between the city and the Chicago Teachers Union are still ongoing, and the union’s president has threatened a strike if their demands aren’t met. They’ve asked for increased staffing, smaller class sizes, and more nurses and social workers. Mayor Lori Lightfoot said she’s working on it, and progress is being made. But Chicago Teacher Union President Jesse Sharkey is calling on the mayor to settle a fair contract. “It’s good that candidate Lightfoot ran on a program of improving our school, delivering services counselors, social workers, those things are important, but now Mayor Lightfoot has to make good on her promises we need it in writing,” CTU President Sharkey said. Meanwhile, CPS opened the new Engelwood STEM High School Tuesday, where more than 400 freshman will be filling its classrooms for the first time. The new $85-million state-of-the-art high school includes multi-purpose educational spaces, modern outdoor sports facility and a school-based health center. Mayor Lightfoot welcomed students to the school Tuesday morning, and held a ribbon cutting ceremony.