Speaker Nancy Pelosi, D-Calif., will endorse Rep. Michael E. Capuano in the Massachusetts Senate special election.

“Whether taking on the CEOs of the financial services industry, supporting marriage equality, or voting against the Iraq War because he didn’t believe Bush Administration made the case to take military action, Mike Capuano has a proven record of standing up for progressive values and what he believes is right. I am proud to endorse Mike Capuano for U.S. Senate,” Pelosi said in a statement. The formal endorsement will come Friday in Boston, Mass.

Capuano, the only member of Congress in the race, has already received the endorsements of five out of the nine other members of the all-Democrat Massachusetts House delegation. Kitty Dukakis, wife of former governor and 1988 Democratic presidential nominee Michael Dukakis, also voiced her support for Capuano earlier this week.

However, the six-term Boston-area congressman continues to trail well behind frontrunner Martha Coakley, the state attorney general, according to a new Suffolk University poll.