Karl Rove's groups are coming under fresh scrutiny. REUTERS

A powerful conservative group that has already poured millions into this election cycle is violating campaign finance laws, the Obama administration charged on Tuesday.

Crossroads GPS, an independent organization founded by a group that includes former top George W. Bush adviser Karl Rove, has established itself as a formidable player in the reshaped world of campaign finance. The organization has spent heavily on advertisements attacking Obama in critical swing states.

The conversation about the deluge of third-party money accompanying this election has mostly surrounded Super PACs, organizations that can raise and spend unlimited amounts of money as long as they do not explicitly coordinate with campaigns. Crossroads GPS is different.

It is a nonprofit 501(c)(4) corporation, a classification that means -- unlike with Super PACs -- it does not have to disclose its donors to the Federal Elections Commission. Crossroads GPS is formed as an educational social welfare group under a special provision in the tax code, which means it cannot have the majority of its activities be political.

The group clearly violates that rule and must therefore reveal its donors, the Obama campaign's chief counsel charged in a complaint to the Federal Elections Commission. Robert F. Bauer wrote in a letter to Rove and to Crossroads president Steven Law that is is obvious to all that Crossroads GPS is a political committee and said that all remains is the issue of when Crossroads will disclose its donors.

If the FEC will not act, it is apparent that the courts will, and we will take action to engage them in the event that the FEC fails to take the prompt, expedited action we are seeking, Bauer wrote. Will Crossroads fight this out, knowing that disclosure is inevitable but looking to delay until after the election?

In the complaint sent to the Federal Elections Commission, Bauer wrote that there has never been any doubt that Crossroads GPS exists to help get certain candidates elected.

Under the pretense of charitable activities, Bauer wrote, Crossroads has tried to shield its donors -- wealthy individuals, and corporations who may be pursuing special interest agendas that are not in the national interest.

Bauer cited a recent ruling, Real Truth About Obama v. FEC, in which the Fourth Circuit Court of Appeals maintained that the Federal Elections Commission must scrutinize organizations like Crossroads to determine their major purpose. If that process is applied, Bauer said, it would reveal that Crossroads GPS is a political entity that must disclose its donors.