Campaign finance reform was supposed to eliminate "soft money" contributions, but many groups have been taking advantage of a loophole in the law — and lawmakers are looking to end the abuse.

So-called 527 groups (search) — named for their IRS designation — operate independently of candidates to fund attack ads and have become a powerful political force, with little accountability.

In Colorado, a 527 called Colorado Families First (search) has spent more than $300,000 on ads against incumbent GOP Rep. Marilyn Musgrave (search).

Guy Short, Musgrave's chief of staff, said the ads are sleazy and in clear violation of the campaign finance law.

"They're an outrageous depiction of the congresswoman," Short said.

Even Musgrave's opponent, Stan Matsunaka (search), agrees the ads are damaging and says his campaign has taken hits, even though he is not behind the group.

"The Law allows 527s to do ads for or against you and so you never know when your friends are helping or hurting you," Matsunaka said.

It's too late to do anything that would curb the influence of 527s in this election cycle, but Sens. John McCain, R-Ariz., and Russ Feingold, D-Wis., the White House and other lawmakers are pursuing legal action to close the 527 loophole in future campaigns.

Click in the box near the top of the story to watch a report by FOX News' Alicia Acuna.