A group that fights for campaign finance disclosures formally filed a complaint with the Federal Election Commission on Monday, claiming that the "super PAC" supporting Mitt Romney is illegally showing an ad from the candidate's 2008 run for president.

Last week, the PAC, Restore Our Future, began rerunning an ad from 2008 about Romney's effort to help find a missing 14-year-old girl in New York City. The only difference between the two ads is that in the old one, Romney says at the end, "I'm Mitt Romney, and I approved this message." In the new one, a woman says, "Restore Our Future is responsible for the content of this message."

The overlap is an example of the muddied rules that are supposed to govern super PACs, nominally independent groups that can spend and raise unlimited amounts of money for candidates. The FEC says that super PACs are forbidden from "coordinating" with campaigns over details on how to spend money for ads, but the regulation is difficult both to enforce and explain.

The Campaign Legal Center took the concrete step on Monday of claiming that the super PAC made "apparent illegal in-kind contributions" by paying for the ad to be shown again. "Such an action would constitute a violation of the law," the group said.

"Restore Our Future's expenditure to republish a Romney campaign ad is considered a contribution from the Super PAC to the Romney campaign under FEC regulations, but Super PACs are prohibited from contributing to candidates," the group's lawyer, Paul Ryan, said in a statement. "The airing of these ads constitutes a clear violation of federal law by the shadow campaign committee Restore Our Future."

A purported violation of the law must be reported to the FEC by a third party because the commission has no policing branch to monitor super PACs or campaigns.

However, it's unlikely that the FEC will act on the complaint in a significant way soon. The FEC can't confirm that it's investigating a case until an investigation is complete, and it could take up to two years. The Republican primaries for Michigan and Arizona, the states where the duplicated ad is running, are on Tuesday.

A spokeswoman for Restore Our Future had no response to the Campaign Legal Center's complaint.

The legal questions underscore the concern that good-government advocates have with super PACs - that they are shadow campaigns run by candidates' allies and former aides.

The board of directors for the super PAC supporting Romney, for example, includes the ex-governor's 2008 campaign lawyer, political director and an ad adviser.

The adviser, Larry McCarthy, told the Daily Beast recently that while the super PAC doesn't coordinate with the campaign, there's no need to.

"We know the Romney team, and they know us very well," he said. "And we're in kind of a mind meld of what we think needs to be done."

The lines are blurred on both sides. After disparaging super PACs for months after the "Citizens United" Supreme Court decision, President Obama recently changed his mind and endorsed the PAC started by two of his former White House aides. Some of Obama's cabinet members are scheduled to speak at fundraising events for the PAC, Priorities USA Action.

At issue with the Campaign Legal Center's complaint is not coordination but a specific rule that the FEC wrote about republishing campaign material.

The regulation says, "The financing of the dissemination, distribution, or republication, in whole or in part, of any broadcast or any written, graphic, or other form of campaign materials prepared by the candidate, the candidate's authorized committee, or an agent of either of the foregoing shall be considered a contribution for the purposes of contribution limitations and reporting responsibilities of the person making the expenditure."