(CNN) - A war of words is erupting in New Hampshire over a pledge from Massachusetts.
The Democratic Senatorial Campaign Committee Monday criticized former Sen. Scott Brown of Massachusetts, who's now taking steps to launch a Republican challenge against Democratic Sen. Jeanne Shaheen of neighboring New Hampshire, for not signing a pledge to keep outside money out of the race.
Follow @politicaltickerFollow @psteinhausercnn
"Scott Brown needs to explain to New Hampshire voters why he chose to honor the People's Pledge in Massachusetts but doesn't think New Hampshire voters deserve the same respect," DSCC Executive Director Guy Cecil said in a statement.
"Brown should follow Shaheen's lead because the decision of who will be the next Senator doesn't belong in the hands of the Koch Brothers who are pushing an agenda that's good for billionaires and bad for New Hampshire. The DSCC will abide by the rules of the People's Pledge if the third party groups supporting Scott Brown do the same," Cecil added.
On Saturday, one day after Brown announced he formed an exploratory committee, an important move which allows Brown to begin raising money and putting together a campaign team in advance of a formal Senate run in New Hampshire, Shaheen sent him a letter concerning the pledge, similar to the one that then-Sen. Brown of Massachusetts signed with Democratic challenger Elizabeth Warren. Brown ended up losing his 2012 bid for re-election.
"I very much admired the People's Pledge that you and Elizabeth Warren signed in your 2012 Massachusetts Senate race. I believe it limited the influence of outside groups and allowed the people's voices to be heard," Shaheen wrote.
"I have signed and attached two copies of an agreement with the exact same terms for the New Hampshire 2014 Senate race. I hope you will join me in once again committing to the same People's Pledge you signed in Massachusetts and limiting the influence of outside groups in New Hampshire this year."
While not commenting on whether he would sign the pledge, Brown responded later Saturday, calling Shaheen's move "self-serving and hypocritical."
"Before I even thought of becoming a candidate, Jeanne Shaheen's allies in Washington were running negative ads against me for months. And right now, while I'm meeting with the people of New Hampshire, she is on the West Coast raising money so third-party groups in DC will have money to run even more outside negative ads against me. It's hard to view Jeanne Shaheen's actions as anything other than hypocritical and self-serving," Brown wrote.
And New Hampshire Republican State Committee Chairman Jennifer Horn wrote that Shaheen's "stunt today represents D.C. politics at its very worst. New Hampshire voters are smart enough to see through Jeanne Shaheen's hypocrisy and double standards."
Shaheen meets with voters across New Hampshire starting Tuesday for three straight days. She spent the weekend fundraising in Washington State and California.
New polls give Shaheen double-digit lead
Brown joins three other Republicans who are running for their party's Senate nomination in New Hampshire: former U.S. Sen. Bob Smith, former state Sen. Jim Rubens, and conservative activist Karen Testerman.
If Brown ends up winning the party's September primary, it could expand the map for Republicans. Democrats hold a 55-45 majority in the Senate (53 Democrats and two independents who caucus with the party), but are defending 21 of the 36 seats up in November, with half of those Democratic-held seats in red or purple states, like New Hampshire.
But a second straight public opinion poll indicates Shaheen has a double digit lead over Brown. According to an American Research Group survey released Monday, 50% of Granite State registered voters say they would support Shaheen, with 38% backing Brown and 12% undecided. The survey indicates Shaheen has a 49%-34% advantage among independent voters.
The poll is similar to a recent Suffolk University/Boston Herald survey that indicated Shaheen has a 52%-39% lead among New Hampshire voters.
From state house to Senate
In January 2010, the then little-known Republican state senator in Massachusetts pulled an upset in a special election to serve the final three years of the late Democratic Sen. Ted Kennedy's term. But Brown's time in the Senate was cut short when Warren defeated him in 2012.
Last year, Scott passed on running in a special election in Massachusetts to fill the term of John Kerry, who left the Senate to become secretary of state. And at the time, Brown also announced that he wouldn't make a 2014 bid for an open governor's seat in the Bay State.
Brown last year made a number of speaking appearances at GOP events in the Granite State, where he spent much of his childhood and where he owned a vacation home. Last fall, in another hint about a possible run, he dropped the 'MA' from his Twitter handle.
A few months later, he sold his home in Massachusetts and moved his residency north to New Hampshire.