BOSTON -- Political action committees and other outside groups are pouring millions into Massachusetts’ U.S. Senate race.
The groups appear to be honoring a deal signed by Republican incumbent Scott Brown and Democratic challenger Elizabeth Warren designed to keep ads from outside groups off television, radio and the Internet.
Instead, the groups are focusing on mass mailings, door-to-door canvassing and automated phone calls -- also known as "robocalls" -- in an effort to appeal directly to voters.
To date, the groups have made more than $2.1 million in "independent expenditures" on the race.
An Associated Press review of reports filed with the Federal Election Commission found that groups supporting Warren and opposing Brown have spent more than $1.3 million so far. That’s almost twice as much as the nearly $800,000 spent by groups supporting Brown and opposing Warren.
The group that has spent the most is the League of Conservation Voters, which opposes Brown’s re-election.
The league, which says it works to elect "pro-environment candidates," has already spent more than $790,000 in Massachusetts and is vowing to spend upward of $1 million before Election Day.
The group announced Wednesday it was spending $200,000 on a new mailing highlighting what the group calls "Scott Brown’s ties to Big Oil" and his opposition to President Barack Obama’s agenda. The effort includes four separate mailings targeting 150,000 households in the state.
The group has already paid dozens of canvassers to go door to door to talk to voters.
Other groups supporting Warren and opposing Brown include the International Association of Firefighters, the United Food and Commercial Workers International Union and a group associated with Emily’s List, which works to elect Democratic women who support abortion rights.
The group that has spent the most opposing Warren is Americans for Tax Reform. The group, which is headed up by anti-tax activist Grover Norquist, has already spent more than $378,000 on mailings to voters.
Norquist is best known for pressing lawmakers to sign a pledge vowing to oppose tax increases -- a pledge that Brown signed during the 2010 special election to fill the Senate seat left vacant by the death of longtime Democratic U.S. Sen. Edward Kennedy.
Another group supporting Brown’s re-election and opposing Warren is Crossroads GPS, an affiliate of American Crossroads, a group with ties to Republican political operative Karl Rove.
The group has reported spending nearly $216,000 on "robocalls" and postage.
Another political action committee supporting Brown is sending out a new mailing with information about how voters can cast absentee ballots in Massachusetts.
The group America 360 -- which has already spent more than $197,000 on political mailers -- announced earlier this week that it was ramping up its efforts on behalf of Brown.
The new mailing, which includes forms voters can use to request absentee ballots, calls Brown a "new independent voice" and says Warren is "hyper-partisan" and out of touch.
Massachusetts allows voters to use absentee ballots when they will be away on Election Day, have a physical disability or can’t vote at polls because of religious beliefs.
The Senate race in Massachusetts is not only one of the costliest in the country, it also features one of the most unusual political agreements in the country -- the so-called people’s pledge signed by Brown and Warren designed to keep ads from political action committees and other outside groups off the airwaves and Internet.
Under the deal, a candidate who benefits from an advertisement from a third-party group has to pay half the cost of the ad to a charity named by the other candidate.
To date, Brown has paid nearly $36,000 to Warren’s charity. Warren hasn’t had to write a check.
In large part, however, the deal appears to be holding with Election Day less than a month off and both national parties keeping a close eye on the contest as they fight for control of the Senate.