Rep. Stephen Lynch (D-Mass.) will run in the special election for Sen. John Kerry's seat, according to several sources familiar with his thinking.

The congressman was expected to announce his plans today. But he told the Boston Globe Friday afternoon that he has not yet decided. The Globe had also reported that Lynch was mounting a bid.

A run would be a surprising move that pits Lynch in the primary against the Democratic establishment.

The Democratic Senatorial Campaign Committee, Vicki Kennedy, Rep. Barney Frank and Kerry himself have all lined up behind Rep. Ed Markey. Lynch also breaks from his party on some key issues -- he's anti-abortion and voted against health-care reform. (He has gone from an opponent to a supporter of gay marriage.) But Lynch was interested in the race early on and has strong ties in the labor movement.

"Lynch's calculation is that if he can grow the primary field and galvanize union voters in a low turnout primary, he has a shot at either victory or a bigger statewide profile," one Massachusetts Democratic strategist said. "He figures he has nothing to lose since he doesn't have to give up his House seat and he's got little to do buried in the House minority."

Assuming Kerry is confirmed as Secretary of State, a placeholder will be appointed by Gov. Deval Patrick (D) until the special election.

Former senator Scott Brown, who lost to Democrat Elizabeth Warren last fall, is considered the strongest Republican candidate.