A Chicago charter school network is seeking help in halting a teachers' strike for much of the past week.

The Chicago Tribune and Sun-Times report Acero filed complaints Friday with the Illinois Educational Labor Relations Board and National Labor Relations Board against the Chicago Teachers Union. The complaint filed in Cook County argues the strike is illegal because teachers didn't follow mediation or notice requirements.

Teachers went on strike Tuesday and classes were canceled for Acero's 15 schools and 7,500 predominantly Latino students. They are demanding smaller classes, more special education staff, salary increases and protections for students and families living in the country illegally.

Union officials say the walkout isn't illegal. They say it's the first strike at any of the privately run, taxpayer-funded schools in the U.S