Teachers prepare for a picket line near a Chicago school Tuesday, starting the country’s first strike against a charter operator. (Antonio Perez/Chicago Tribune/AP)

The nation’s first teachers strike against a charter school operator will end after their union and management struck a tentative deal Sunday that includes protections for students and immigrant families living in the country illegally.

The Chicago Teachers Union said more than 500 teachers will return to classes Monday at Acero’s 15 schools, with 7,500 predominantly Latino students. Teachers went on strike Tuesday, and classes were canceled.

Robert Bloch, general counsel for the union, said that because the schools’ enrollment is “overwhelmingly low-income Latino,” the union thought it was necessary to have provisions to protect students, their families and teachers who may be living in the country illegally. The agreement prohibits Acero from collecting and distributing information about the immigration status of students, teachers and families and restricts access by Immigration and Customs Enforcement to schools except by court order, he said.

Acero said in a news release that the two sides agreed to give teachers and staff members annual raises over the four-year term of the contract, and the charter operator agreed to the union’s request to shorten the school year to more closely align with Chicago Public Schools.

Teachers’ work days will be reduced, but Acero said that through changes in the way the school day is structured, the schools will preserve the amount of instructional time. The deal was struck just before 5 a.m. Sunday.

“Thanks to hard work and very long hours from both bargaining teams, we were able to reach an agreement that values teachers and staff for the important work they do, while still maintaining the attributes of our network that help produce strong educational outcomes for our students,” Acero chief executive Richard L. Rodriguez said in a prepared statement. “Most important for all of us and the families and communities we serve, we can now get students back into the classroom, where they belong.”

The union said the agreement also reduces class sizes.

It said the strike was the first against a charter school operator in the nation. The union also represents public school teachers in Chicago.