The Chicago Teachers Union has filed an unfair labor practice complaint against the school district.

It comes just days before teachers could walk out on strike.

The complaint stems from the paychecks teachers received at the end of August. 

Those checks did not include annual “step” raises that teachers were scheduled to get under their old contract for experience on the job.

Technically, teachers are still working under the terms of their expired contract.

Union President Karen Lewis says teachers are entitled to their money: “It is a decrease in pay for our members. Our members have been getting step raises for 40 years.”

The school district wants to completely eliminate step raises. It argues there’s a better way to distribute raises—for instance, by giving more money to teachers who take on more responsibility.

“We object to the school board trying to force teachers to accept something that hasn’t been achieved at the bargaining table,” said union lawyer Robert Bloch.

Filing the complaint offers teachers a protection they would not have otherwise. Bloch says any strike will now become a strike over unfair labor practices, and not simply a contract strike. That prevents the district from hiring permanent replacements for teachers on the picket line.

The district dismissed the union’s complaint as “antics” and “unnecessary litigation.” It said the union should focus on negotiations.

In other news, the union’s House of Delegates met Wednesday for an update on contract negotiations. Delegates could have altered the strike date but did not. The union says it will walk out on Monday if it does not have a contract agreement. Lewis said Wednesday she’s  “very optimistic” the two sides will reach an agreement without a strike, even as teachers left the meeting carrying bags of red union T-shirts and picket signs.