CNN

Lieberman is co-hosting a fundraiser for Republican Sen. Susan Collins Thursday.

Washington (CNN) – A fundraiser Thursday night for Sen. Susan Collins, R-Maine, is drawing heat from liberals due in large part to the event’s co-host: Sen. Joseph Lieberman, I-Connecticut.

In an e-mail sent to supporters, the anti-war group MoveOn.org called tonight’s event “absurd,” labeling it “Joe Lieberman’s Republican fundraiser.” The event, which will be held in Washington, is being co-hosted by Lieberman and Republican Sen. Arlen Specter of Pennsylvania.

MoveOn.org is working to counter Lieberman’s efforts by raising money for Collins’ 2008 Senate opponent, Democratic congressman Tom Allen. As of Thursday afternoon, MoveOn had raised over $200,000 for Allen in just over 48 hours. Allen’s campaign said it welcomed the support.

Over the past several years, Lieberman’s support for the war in Iraq has made him a marked man among liberal bloggers. His reputation on the Web bottomed out last year during his contentious Senate race with millionaire businessman Ned Lamont, an anti-war Democrat. Thanks largely to the support of prominent liberal bloggers, Lamont upset Lieberman in the Connecticut Democratic primary last August. Lieberman then switched his party affiliation to Independent and was re-elected to the Senate in November.

Collins endorsed Lieberman at the time, and the two senators have worked closely together on the Senate Homeland Security and Governmental Affairs committees.

“Senator Lieberman is very pleased to support Senator Collins because she is an extremely effective senator who works in a bi-partisan fashion to get things done,” said Lieberman spokesperson Marshall Wittman. “Senator Lieberman strongly believes that the American people want progress before partisanship.”

A spokesperson for Collins called Allen an “extreme party loyalist” and dismissed the MoveOn fundraising effort.

“The event that Senators Specter and Lieberman are hosting for Senator Collins tonight strikes a blow at those who thrive on base-driven politics and hyper-partisanship,” said Collins spokesperson Jen Burita in an email. “Senator Collins is proud to have support of Senators Specter and Lieberman and looks forward to tonight’s event.”

– CNN Associate Producer Peter Hamby