CHICAGO (AP) – The nation’s first teachers’ strike against a charter school operator is ending in Chicago.

The Chicago Teachers Union says more than 500 teachers will return to classes Monday at Acero’s charter schools after reaching the tentative agreement just before 5 a.m. Sunday. The union said in a news release the deal “aligns” pay for teachers with pay scales in the Chicago Public Schools over the course of the agreement, reduces class sizes and includes language setting terms for students and families living in the country without legal permission.

Teachers went on strike Tuesday and classes were canceled for Acero’s 15 schools with 7,500 predominantly Latino students. The union said the strike was the first against a charter school operator in the nation.