BOSTON (AP) — The two Democratic candidates in the Massachusetts' special U.S. Senate election are touting competing union endorsements.

On Thursday, Stephen Lynch announced he's holding a press conference in Boston's Brighton neighborhood Friday to accept the backing of the Boston Police Patrolmen's Association, the Massachusetts Coalition of Police and the International Brotherhood of Police Officers.

Less than an hour after Lynch announced the police union endorsements, fellow congressman and Democratic rival Edward Markey announced the endorsement of the United Steelworkers, District 4.

A short time, later, Lynch sent out another press release saying he was proud to have the support of the United Steel Workers, Local 12003.

The sparring for endorsements shows the importance both candidates place on union backing in the April 30 primary election.

There are three Republicans vying for their party's nomination.