Hundreds of teachers in Dedham, Massachusetts violated their contracts when they picketed during hours they were supposed to be working. That was the finding of the Massachusetts Labor Relations Commission last week. The ruling says that because the teachers left work early and arrived at their classes late because of picketing plans, they were essentially striking, a violation of their contracts. It is illegal for public employees to strike in Massachusetts. The suit was filed by the School Committee. The two sides have been negotiating since January of 2004.