Chicago Teachers Union, which represents the city's 25,000 school educators, has been locked in negotiations with Chicago public schools for months over the gradual reopening of schools for the systems 355,000 students.

The labor dispute came to a head on Sunday when the union membership voted 71% in favor of a resolution not to return to the classroom and to remain teaching remotely until a stronger health and safety agreement is reached.

Despite the vote, the district ordered some 10,000 teachers to report to work on Wednesday instead of Monday as initially planned.

Some 70,000 elementary and middle school students who opted to take classes both in person and online, are due to return at the beginning of next week.

As of early Wednesday afternoon, it was unclear how Maney teachers reported for work at their schools.

Chicago Public Schools CEO Janice Jackson warned on Sunday that if teachers did not report to schools on Wednesday, it would be construed as an illegal strike.

In a message to teachers on Tuesday night, the union said that if the district takes action against teachers who did not report, members will stop working altogether on Thursday and picket, The Chicago Tribune reported.

Similar labor battles have unfolded across the country, pitting teacher unions against district officials over conditions for reopening almost a year after the virus shut down schools for 50 million students nationwide.