CHICAGO (AP) — Chicago extended remote learning for tens of thousands of public school students after city, school and teachers’ union officials on Wednesday were once again unable to reach an agreement over COVID-19 safety protocols.

In a statement, Chicago Public Schools expressed disappointment that no deal was reached between the district and Chicago Teachers Union leadership. District officials said a cooling off period will be extended through the end of the day Thursday to allow for further negotiations. Students have Friday off.

The nation’s third-largest district has pitched a gradual return for pre-K to 8th grade students with no definite plans yet for high school students. But the Chicago Teachers Union said the district’s safety plan doesn’t go far enough to protect teachers.

The fight to reopen city schools, which went remote last March, has brewed for months. The nation’s third-largest district pitched a gradual return for pre-K to 8th grade with no definitive plans for high school. But the Chicago Teachers Union said the district’s safety plan falls short.

Earlier in the week, Mayor Lori Lightfoot said teachers who didn’t report for duty would be locked out of online teaching systems, as was the case for pre-K and special education teachers who defied orders last month. The 25,000-member union countered by saying it would picket if teachers were booted out. But district officials scrapped the threat and called “cooling off period.

“Discussions continue between CPS and CTU. We will provide an update as quickly as possible,” read a statement Wednesday from Mayor Lori Lightfoot and the district’s CEO Janice Jackson.

Union spokeswoman Chris Geovanis declined comment, saying the union would have an update Thursday.

Among the issues are vaccinations, allowing educators to continue remote instruction if they have a valid excuse and different metrics to gauge infections.

Students in K-8 were supposed to return earlier this week for two days a week of in-person instruction. Thousands of pre-K and special education students started last month, but switched back amid the escalating fight with the union.

District officials argue remote learning isn’t working well for all, particularly many Black and Latino students who are the majority of the roughly 340,000-student district.

The district has spent roughly $100 million on its safety plan, including purchasing air purifiers, deep cleaning schools and offering COVID-19 testing for teachers.

But the union, which last went on strike in 2019, says infections continue and the safest option is online learning. They also argue few students are interested in returning. Less than 20% of pre-K and special education students eligible to return to class last month, or about 3,200 of 17,000, attended.

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