Chicago (CBS)–Teachers at the four Chicago International Charter Schools are on strike.

At CICS Wrightwood, teachers will be absent from the classrooms Tuesday as they walk the picket line.

The decision came after months of negotiations without a deal.

The Chicago Teachers Union says the charter operator isn’t putting money where it’s needed, and it’s not paying teachers what they’re worth.

CICS released a statement saying it’s “deeply disappointed that the Chicago Teachers Union has chosen to strike.

The strike will place a significant burden on families with students at the four schools.

CICS says it offered salary increases, more paid time off… and class sizes that would be capped at 29 students.

All four campuses will remain open Tuesday, with principals and non-union staff leading online learning activities.