The socially conservative Democrat also emphasized his differences with rival U.S. Rep. Edward J. Markey, the party favorite, the Boston Globe reported.
Lynch noted his opposition to privatizing Medicare and Social Security, and said he was one of only two members of the state's congressional delegation to vote against the Wall Street bailout.
After campaign stops in Springfield and Worcester, he was scheduled to make an official announcement at an ironworkers union hall in South Boston, the Boston Herald reported.
Lynch was an ironworker for 18 years before running for office.
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