By Emily Cadei, CQ Staff

A handful of interest groups are waging a high-spending campaign battle in the last days of the 2008 election.

On the Republican side, the conservative National Republican Trust PAC grabbed attention over the weekend with an ad questioning the ties between Democratic presidential candidate Barack Obama and his controversial ex-pastor Rev. Jeremiah Wright. The group, which was formed in mid-September by journalist and Army veteran Scott Wheeler, has spent $4.3 million since Thursday on the ad buy, as well as on e-mail and phone messages, and online ads opposing Obama.

Also on the Republican front lines is the business-backed nonprofit group Americans for Job Security. The group dropped $1.2 million Oct. 30 on ads critical of Democratic Senate candidates Al Franken in Minnesota and Ronnie Musgrove in Mississippi, as well as Democratic Rep. Steve Kagen in Wisconsin.

The group’s ad against Franken claims he is partly to blame for the current financial crisis, saying the Democrat “encouraged sub-prime lending.”

Countering the conservatives are the labor unions. The Service Employees International Union spent $1.6 million through its political action committee, SEIU COPE, over the weekend in support of Obama and other Democrats. It spent another $577,000 from its general treasury on issue ads critical of Republican presidential nominee John McCain .

One SEIU-funded ad, running in Ohio, criticizes the Arizona Republican for supporting “policies that give tax breaks to CEOs and Wall Street executives instead of hardworking Americans.”

Donations from the International Brotherhood of Teamsters and the United Food and Commercial Workers International Union also helped fund a $455,000 ad buy made on Friday by the nonprofit group Citizens for Strength and Security. It hits at Senate Minority Leader Mitch McConnell , R-Ky., for his support of trade agreements.