Since January 2010, spending by outside organizations to influence congressional elections totals some $57 million–up more than $20 million from a comparable time period in 2006, the most recent non-presidential election cycle–according to reports collected by the Federal Election Commission. 

Though the rising independent expenditures–money spent by outside groups on anything from phone banks and mailing lists to negative political ads to influence a federal election–come after the Supreme Court decisions that weakened campaign finance laws, it's unclear whether those rulings are fueling the boom.

While some labor unions have taken advantage of the rulings to directly make independent expenditures, corporations have yet to. And some of the biggest spenders are Republican and Democratic party committees not affected by the court decisions. But there are more than thirty political organizations that have filed documents with the FEC declaring their intention to receive unlimited contributions from any source to influence the 2010 mid-term elections.

To track all these independent expenditures, and the groups that make them, in real time the Sunlight Foundation Reporting Group is releasing a new tool to Follow the Unlimited Money, available on our home page now. The tool allows users to search independent expenditure filings by organization, candidate and race.

Although so far there is no indication that money from corporations is flowing to influence an election in FEC reports, there is a spike in spending by labor unions. Overall, among the top four organizations making independent expenditures are two labor unions, the Service Employees International Union ($7.2 million) and the American Federation of State, County and Municipal Employees ($5.8 million). In 2006 these two labor unions spent only $303,000 and $4.5 million respectively, though they did contribute millions more to other political organizations that focused on federal candidates.

A pair of party committees–the National Republican Congressional Committee and the Democratic Senatorial Campaign Committee–round out the top four.

During the same nine-month period from January to September in 2006, the last mid-term election, outside groups spent $35.3 million, according to an official with the FEC–far less than the $57 million in 2010. And with more than five weeks to go before the mid-term elections, independent expenditures will likely run that total much higher.

So far, leadership PACs and official party committees like the Democratic Senatorial Campaign Committee and the National Republican Congressional Committee have been among the top spenders in some races around the country–the sources and amounts of the contributions these organizations can take are limited by federal election law.

Outside groups have focused their spending on close races. For instance, the Arkansas Senate race involving incumbent Blanche Lincoln and challenger Bill Halter in the primary and Republican nominee John Boozman, has seen the greatest amount of independent money spent so far at just under $8 million. Halter, the state’s Lieutenant Governor, forced Lincoln into a runoff when neither candidate won 50 percent of the vote in the primary. Outside groups, including SEIU and Working America, an affiliate of the AFL-CIO, spent more than $4 million spent to support Halter. Labor unions also spent $2.3 million on ads opposing Lincoln. Despite the substantial amount spent in his favor, Lincoln defeated Halter.

The Colorado Senate race pitting Democratic incumbent Michael Bennet against the tea party-supported Republican nominee, Ken Buck, has also drawn substantial attention, ranking fourth among elections with the most outside spending. Outside groups have spent $3.4 million to influence that election. The Senate Conservatives Fund, a leadership PAC set up by Sen. Jim DeMint, R-S.C., has spent $140,000 supporting Buck, while the Democratic Senatorial Campaign Committee, the official party committee of Senate Democrats, devoted $1.67 million to defeating him. The League of Conservation Voters Fund, SEIU and Working America are supporting Bennet, while Amerian Crossroads–Karl Rove's highly publicized group–and the Club for Growth have opposed him. Overall, outside groups have doled out $311,000 to reelect Bennet and $1.3 million to retire him.  

In the Missouri Senate race, American Crossroads is spending $340,000 to oppose Democrat Robin Carnahan, currently Secretary of State–more than ten percent of the $3.2 million in independent expenditures spent on the race. Roy Blunt soaks up a great deal of that money with over $2.5 million spent against him by several groups including League of Conservation Voters and Women Vote!; Blunt has drawn only $21,000 from groups to support him. 

The defeated Democratic incumbent from Pennsylvania, Arlen Specter, only had a total of $55,000 in independent money spent in support and opposition of him, while the overall total in that Senate race is $3.1 million. Pat Toomey, the Republican nominee absorbs the bulk of this spending with $2.5 million spent in opposition of him and just $53,000 spent to support him. Joseph Sestak, Jr., the Democratic nominee, has had $469,000 spent against him and $62,000 spent to support him.  

The special election that put republican Scott Brown in office in Massachusetts had the seventh greatest amount of money spent at $3 million. Martha Coakley’s failed attempt for Senate seat was aided by $1.5 million spent to support her, while Brown’s successful attempt was helped by $1.3 million. 

The Sunlight Foundation Reporting Group conducted this analysis using records released by the FEC. To see our comprehensive database containing all independent expenditure money, click here. 

Aaron Bycoffe contributed to this report.