UNITED STATES - FEBRUARY 27: Sen. Elizabeth Warren, D-Mass., attends a Senate Banking, Housing and Urban Affairs Committee hearing in Dirksen Building titled the 'Semiannual Monetary Policy Report to the Congress.' Janet Yellen, Chairman of the Federal Reserve, testified. (Photo By Tom Williams/CQ Roll Call)

WASHINGTON -- Sen. Elizabeth Warren (D-Mass.) is headed to Oregon next month to help secure the reelection of one her fellow progressives, Sen. Jeff Merkley (D-Ore.).

Warren and Merkley will hold a grassroots fundraiser in Portland at 12:30 p.m. on May 28 at the Hilton downtown.

"I'm proud to have Elizabeth's support and glad Oregonians are going to have a chance to see up close how terrific she is,” Merkley said in a statement provided to The Huffington Post. "She is a champion for working people across this nation and a close ally of mine on so many issues, from the battle to reform Wall Street to our fight to bring down the cost of college loans. It's a privilege seeing her in action in the Senate and I'm glad to have her join me here in Oregon."

Merkley has become a key voice for progressives in the Senate, spearheading the push for filibuster reform and introducing the Employment Non-Discrimination Act, which passed the Senate with bipartisan support. He also led the opposition to Larry Summers becoming chair of the Federal Reserve.

In 2010, Merkley was a leading advocate for Warren to chair the Consumer Financial Protection Bureau. The admiration is mutual; when Merkley gave the keynote address last year at Netroots Nation, an annual gathering of progressive activists, Warren called him her "mentor" and "friend." At a recent stop on her book tour, Warren cited Merkley, along with Senate Majority Leader Harry Reid (D-Nev.) and Majority Whip Dick Durbin (D-Ill.) as three colleagues who have been "particularly helpful" in the chamber.

Although Warren is not up for reelection this year, she's a key figure in Democrats' attempts to keep control of the Senate. She's already raised over a million dollars for 22 Senate candidates this cycle. Last month, she went to Minnesota to campaign for Sen. Al Franken (D-Minn.).