PENN HILLS — More than 400 teachers in one of the Pittsburgh area's biggest school districts say they'll go on strike Thursday over a contract impasse.

The Penn Hills Education Association is upset because they say contract proposals by the school board include a wage freeze and for teachers to contribute more to pay for their health insurance.

The school board says the district can't afford more and is trying to avoid raising taxes.

By law, the teachers will only strike for a few days because they must return to class in time for students to receive 180 days of instruction by June 15.

Their last contract expired Aug. 31, and both sides have began negotiating months before that, in October 2008.