Mayor Lori Lightfoot and Chicago Public Schools CEO Pedro Martinez said in a joint statement Sunday evening that there wasn’t “sufficient progress” in talks to resume in-person classes Monday, extending disruptions into a second school week. But they vowed negotiations would continue “through the night.”

Disputed issues included testing and metrics to close schools. The Chicago Teachers Union wants the option to revert to districtwide remote instruction, and most members have refused to teach in-person until there’s an agreement, or the latest COVID-19 spike subsides. But Chicago leaders reject districtwide remote learning, saying it’s detrimental to students and schools are safe. Instead, Chicago opted to cancel classes as a whole two days after students returned from winter break.

Chicago faces the same pandemic issues as other districts nationwide, with more reverting to remote learning as infections soar and staff members are sidelined. But the situation in union-friendly Chicago has been amplified in a labor dispute that’s familiar to families in the mostly low-income Black and Latino district who have seen disruptions during a similar safety protocol fight last year, a 2019 strike and a one-day work stoppage in 2016.

The announcement for the roughly 350,000-student district came as the principals of some schools had already notified families their schools would be closed for instruction Monday because of staffing shortages.

The tone of Lightfoot and Martinez’s Sunday evening statement suggested more progress than a day earlier when shortly after the union made its latest offer public, they said, “CTU leadership, you’re not listening” and vowed not to “relent.” The offer she rejected included teachers reporting to schools Monday to distribute laptops for remote learning to temporarily start Wednesday. Both sides have filed complaints to a state labor board.

Union leaders have accused Lightfoot of bullying, saying they agree that in-person instruction is better, but the pandemic is forcing difficult decisions. Attendance was down ahead of the cancelations due students and teachers in isolation from possible exposure to the virus and families opting to keep children home voluntarily.

“Educators are not the enemy Mayor Lightfoot wants them to be,” the union said in a statement Sunday, adding that the desire to be in the classroom “must be balanced by ensuring those classrooms are safe, healthy and well-resourced, with the proper mitigation necessary to reduce the spread of COVID-19.”

Union leaders did not immediately have a response after the district’s Sunday evening cancelation.

There appeared to be some headway over the weekend toward a deal.

The district, which deems the fight an “illegal walkout,” said late Saturday it will allow more incentives for substitute teachers, provide KN95 masks for all teachers and students, and that Illinois will provide about 350,000 antigen tests. But both sides remained at odds on key issues including COVID-19 metrics that will lead to individual school closures and compensation. The district said it won’t pay teachers failing to report to schools, even if they tried to log into remote teaching systems. The union doesn’t want any of its roughly 25,000 members to be disciplined or lose pay.

District leaders had said some schools, where enough staff showed up, may offer instruction Monday even without an agreement; all buildings have remained open for meal pickup. However, only a handful of principals anticipated having staff to open.

School leaders have touted a $100 million safety plan, which includes air purifiers in each classroom. Also, roughly 91% of staff are vaccinated and masks are required indoors.

Since the start of the academic year, some individual classrooms have temporarily switched to remote instruction when there are infections. But in rejecting a widescale return to remote learning, city health officials argue most students directed to quarantine because of possible classroom exposure don’t get COVID-19. The district is piloting a “test to stay” program to cut isolation times.

The union argues that the measures fall short, especially considering the omicron-fueled surge that has upended the return to work and class. It has also criticized the district for not enrolling enough students in a testing program and an unreliable database of COVID-19 infections.

Several district families, represented by the conservative Liberty Justice Center in Chicago, filed a lawsuit in Cook County over the closures last week, while more than 5,000 others have signed a petition urging a return to in-person instruction.