CHICAGO • Leaders of Chicago Public Schools canceled classes Wednesday after the teachers union voted to refuse in-person instruction and switch to remote learning due to the surge in COVID-19 cases, the latest development in an escalating battle over pandemic safety protocols in the nation’s third-largest school district.

Chicago has rejected a districtwide return to remote instruction, saying it was disastrous for children’s learning and mental health, and the status of instruction for the rest of the week was in limbo. The union argued that the district’s safety protocols are lacking, and teachers and students are vulnerable.

Children in the roughly 350,000-student district returned to class Monday after a two-week winter break with COVID-19 infections and hospitalizations fueled by the omicron variant at record levels. School districts nationwide have grappled with the same issue, with most opting to stay open while ramping up virus testing, tweaking protocols and other adjustments in response to the shifting pandemic. White House press secretary Jen Psaki, echoing President Joe Biden a day earlier, said Wednesday that the country is better equipped now to make sure schools can safely open “including in Chicago,” while former President Donald Trump called the closures “devastating.”

Chicago Teachers Union President Jesse Sharkey said the union planned to meet with district officials Wednesday. But he said teachers don’t want to return to in-person instruction until the current surge has subsided.

“We’d rather be in our classes teaching, we’d rather have the schools open. What we are saying though is that right now we’re in the middle of a major surge,” he said during a news conference with other union officials, teachers and parents.

The union’s action, approved by 73% of members, called for remote instruction until “cases substantially subside” or union leaders approve an agreement for safety protocols with the district. The district said early Tuesday that classes would be canceled Wednesday if the union voted not to return to in-person instruction.

Devices were not distributed to students ahead of the union vote, which was announced just before 11 p.m. Tuesday. Union members who tried to log into teaching systems Wednesday said they were locked out.

District officials blamed the union for the late cancellation, saying despite safety measures including a high teacher vaccination rate, “our teachers are not willing to report to work.”

“We are deeply concerned about this decision but even more concerned about its impact on the health, safety, and well-being of our students and families,” the district said in a statement.

CPS leaders said a plan would come later Wednesday to “continue student learning” in the district, where students are largely low income and Black and Latino. School officials labeled the union action an “illegal work stoppage” and said those who did not report to schools Wednesday would not be compensated.