Chicago Public Schools jumped an initial legal hurdle Thursday to have the Chicago Teachers Union’s April 1 strike declared illegal after a state board agreed to hear the school district’s case, which asks the union to pay strike damages.

And days before the union and district will learn how a fact-finder thinks they should settle their ongoing contract dispute, the Chicago Board of Education announced it would withhold a $250 “spring break bonus” from some of its lowest-paid workers.

The Illinois Educational Labor Relations Board will consider CPS’ complaint on April 21 at its monthly meeting. The district has sued the union for costs resulting from the strike — such as the contingency plans CPS made for children. CPS still won’t say how much those plans cost.

The district told the appointed state board that the union isn’t legally allowed to strike before fact-finding ended, and the fact-finder’s report is due to CPS and the CTU on Saturday. The CTU disagrees, saying teachers could strike over unfair labor practices under federal — not state — law.

The unfair labor practice cited was CPS’ cancellation of teacher raises at the start of the school year. The district contended it did not have to pay them while teacher pay was still being negotiated.

Union officials were outraged about the elimination of the $250 bonus paid for more than a decade to those who work as school clerks, teacher’s assistants and other school-based helpers.

In an action alert sent out to members, the CTU blasted “the move that will net the district less than one ten-thousandth of its annual budget” and vowed to “use every tool at our disposal to fight this.”

“This attack will only hinder CPS in negotiations and make angry CTU members ready to fight harder,” the union said.

CPS spokeswoman Emily Bittner said about 3,500 workers received the bonus in 2015 at a cost of about $875,000.

“Much like the practice of COLAs, steps and lanes, CPS will not continue to provide payments that are currently subject to negotiation, but did incorporate additional PSRP compensation in the tentative agreement we reached with CTU leadership in January,” she said in a statement.