Nearly 400 teachers and professional support staff are on strike in the Bethel Park School District.
The American Federation of Teachers represents the 391 striking teachers and staff in the Bethel Park School District.
The school district posted a notice on its Web site that classes were cancelled indefinitely due to the strike.
The sides have been negotiating since January but have been unable to reach a new contract since the old one expired June 30. The union voted to authorize a strike in August, but negotiations continued until they broke down over the weekend.