Washington Teachers’ Union and D.C. Public Schools representatives spent Thursday in front of a mediator weighing charges that the city breached its agreement with the union over how to reopen schools.

A ruling in the union’s favor could jeopardize parts of the city’s already complicated push to resume in-person learning on Monday. Both groups said they expect a ruling before school starts.

The union alleges the District has not met all safety guidelines outlined in the agreement signed last month, and it also says the city needs to share more school-specific data on the number of students returning to campuses. The union fears the city is calling for more teachers to return than necessary. Under the agreement, schools that do not adhere to the guidelines that cover safety and staffing issues are not allowed to reopen.

D.C. Public Schools Chancellor Lewis D. Ferebee called it the union’s “last-resort effort to prevent schools from reopening” and said the complaints were “meritless.” He has said schools will reopen Monday.

“We have spent many months and millions of dollars to prepare,” he said in a statement. “We know our students are ready, we know our buildings are ready, and we know our staff is ready and efforts to reopen schools on Monday will continue as planned.”

If the arbiter does not rule in the union’s favor — or takes too long to rule — Washington Teachers’ Union President Elizabeth Davis said she is considering seeking an injunction, which she believes could delay the reopening of schools.

The city does not need an agreement with the union to reopen, but an agreement would make it more likely that teachers will show up to school buildings Monday. The city canceled its November reopening plans after it failed to reach an agreement with the union.

Davis said calling for an emergency hearing with an arbiter was a necessary step to ensure that school buildings are safe for students and staff. She said some of her members have found violations on walk-throughs of the buildings, including inadequate supplies in bathrooms and HVAC systems that lack documentation showing they have been repaired and upgraded.

She has also said the school system needs to share more detailed data on the demand for in-person learning so she understands just how many teachers are required.

Around 8,000 students across all grade levels have accepted slots to return to school buildings next week for in-person schedules that range from one day a week to every day. The city has called back around 1,800 teachers and 1,960 support staff members.

The agreement also said any dispute with compliance must be mediated through the American Arbitration Association, an independent organization.

City officials said the union’s allegations do not point to systemic issues with the school system’s adherence to the agreement. Even if the arbiter determined the school system did not fully follow a provision — such as a maintenance issue at a school — they are confident it can be fixed before Monday.

“The issues that they raised can and will be addressed if needed,” said John Falcicchio, the mayor’s chief of staff. “What we do not want to experience over the next few days is a moving of the goal posts.”

Davis held out the possibility of filing an injunction, depending on what happens with the arbiter.

“I would file an injunction because it is urgent and it is around safety and health,” Davis said. “Both teachers and parents want to know if buildings are safe.”

The union is planning a series of protests Saturday calling for a delay to reopening.