The District’s public school system was close to an agreement with the Washington Teachers’ Union on the safety precautions the city would need to take to reopen classrooms during the pandemic, but negotiations stalled over details in the plan to ensure that the buildings were safe.

After hours of virtual negotiations Wednesday, both union and city officials said they expected an agreement to be signed Thursday. Mayor Muriel E. Bowser (D) was optimistic, saying at her news conference Wednesday that the city and the union have a “large agreement on how to reopen.”

But Thursday afternoon, after more negotiations, the union announced it was not satisfied with part of the plan. The setback comes less than a month before some elementary students are expected to return to classrooms. Schools Chancellor Lewis D. Ferebee does not need an agreement with the union to move forward with reopening schools, but it would make it more likely that teachers would say they are willing to return to classrooms.

School officials said they are optimistic that they will strike a deal and will continue to negotiate. The union also said it would continue to negotiate.

An accord would have been a notable step for the city and the union, which have disagreed bitterly and often publicly on the details and process of returning students to classrooms since schools closed in March.

The plan focused on building safety and left many key and contentious questions unanswered, including what job security teachers will have or what the city would do if a large swath of the workforce does not want to return to physical classrooms. The disputes Thursday that stalled the agreement were largely about who is included in the process to verify that each building has met the agreed-upon safety criteria. Washington Teachers’ Union President Elizabeth Davis wrote in a statement Thursday that the union is still negotiating a few safety protocols.

“In the absence of immediate corrections to shortcomings in our school environments, it is our belief that school buildings should be closed in order to protect our community,” she wrote.

The proposed five-page agreement states that each school will be stocked with masks for teachers and students and that teachers will be given a new face shield every week. There will be a quarantine area in each building for students and teachers who exhibit symptoms during the day, according to the memorandum of agreement shared with The Washington Post on Wednesday evening.

Initially, the Washington Teachers’ Union had sought hazard pay and a suspension of standardized testing and teacher evaluations. These were big asks that exceeded the reopening demands laid out by the American Federation of Teachers, the national union. The chancellor and the union did not agree to them during these negotiations, and these were not included in the agreement that was expected to be finalized Thursday.

The union had also laid out in its initial demands that teachers should not be required to return to in-person learning during the pandemic. The proposed agreement Wednesday did not say that in-person teaching is optional.

But the union did already win on a significant point, according to Davis. Any school building that fails to meet the agreed-upon criteria — which the two groups are calling a “safety checklist” — would not reopen for in-person learning. The groups are still debating who gets to be a part of the process to determine that every school adheres to the safety checklist and what the reporting protocol will be if there are any violations.

The agreement also says that, to reopen, every HVAC system must be upgraded to a filter that has a Minimum Efficiency Reporting Value, or MERV, of at least 13, which industry standards deem effective at removing particles from the air. Teachers can request documentation to verify that the filters in their buildings have been upgraded and inspected.

The union had asked for a nurse at every school. The agreement said there would be a “health care professional” on each campus. Davis said she received no details on who qualifies as a health-care professional but said it reassures her that teachers will not be responsible for administering the daily temperature checks when students enter the building.

“We do know that there are extenuating circumstances in regards to their budget and what they can do,” Davis said. “We want to be reasonable in our asks, and we made concessions.” 

Davis said the union is still seeking avenues to its other goals, including on the use of teacher evaluations and any requirement that teachers return to the classroom. One option, she said, is to file labor grievances at the Public Employee Relations Board. And it’s possible that Ferebee and Davis will need to return to the negotiating table as reopening plans progress.

Most of the elementary students who would be invited back to campus next month would be supervised by nonteaching staff, participating in virtual learning from their classrooms. This suggests that the city did not believe it could persuade ample teaching staff to return to classrooms.

The plan was met with widespread condemnation from teachers, who said they were left out of the plans to reopen and said there were too many unanswered questions about logistics around safety protocols.

The school system has since informed its central office employees — who are not unionized — that they may be called to classrooms to supervise children, according to documents shared with The Post.

The chancellor has previously said that he would implement many of the safeguards laid out in the agreement, but Davis said the workforce has been skeptical that the city will do what it has said to make buildings safe.

“There are huge trust issues in the District,” Davis said. “And the chancellor needs to understand that.”

Julie Zauzmer contributed to this report.