A watchdog group on Wednesday asked the Justice Department to investigate two “super PACs” helping President Obama and GOP challenger Mitt Romney, alleging that the groups are “engaged in illegal activities” by coordinating too closely with the presidential campaigns.

The complaint from Democracy 21, headed by longtime campaign finance reform activist Fred Wertheimer, follows announcements from the Obama and Romney campaigns that they would encourage surrogates to appear at super PAC fundraising events.

Super PACs, a recently created type of political group that can raise and spend unlimited funds, have already had an enormous impact on the Republican primary race by outspending the candidates in some states.

The groups are supposed to be independent from candidates and are prohibited from coordinating directly with campaigns on issues such as where and when to run advertisements. But the two campaigns, citing rulings from the Federal Election Commission, have said they believe they are legally allowed to take part in fundraisers held by super PACs and to encourage support for the groups in other ways.

In his letter to the Justice Department, Wertheimer disagrees and argues that both the Obama and Romney camps are overstepping the bounds of what they are allowed to do “in a flagrant and willful fashion.”

“Democracy 21 believes that the Super PACs supporting President Obama and presidential candidate Romney are violating the law and need to be held accountable,” Wertheimer wrote. “...[T]he web of ties and connections between the Super PACs and their respective candidates is in clear contravention of the standard for independence established in multiple Supreme Court decisions and in the federal campaign finance statute.”

Charlie Spies, treasurer for Restore Our Future, a pro-Romney super PAC, said in a statement that “Wertheimer has a long history of making hyperbolic accusations to gain publicity for himself and fundraise for his lobbying organization.”

“His current frustration appears to be with the effect of the McCain-Feingold law that he supported as well as First Amendment free speech protections,” Spies said, referring to campaign-finance legislation. “Like all American citizens, he is welcome to petition Congress to amend the First Amendment or change current law.”

Bill Burton, a spokesman for Priorities USA Action, a pro-Obama super PAC, said: “We operate in full compliance of the rules and laws that govern campaign finance.”

The Obama and Romney campaigns declined comment. The Justice Department declined comment.

Wertheimer’s letter marks the latest volley in a raging debate over the looser campaign finance rules that have unleashed tens of millions of dollars from wealthy individuals and corporations into the 2012 elections.

A series of decisions, including a Supreme Court ruling in Citizens United v. FEC, has made it far easier for well-funded interests to influence elections through donations to lightly regulated outside groups such as super PACs. Restore Our Future has spent millions to bolster Romney in the GOP primaries, while Republican candidate Newt Gingrich has been aided by $11 million from casino magnate Sheldon Adelson and his family.

Obama, who has frequently inveighed against the role played by money in politics, announced last week that his campaign would cooperate more directly with Priorities USA by allowing aides and Cabinet members to appear at events. The campaign portrayed the move as a necessary step to combat spending by independent conservative groups, which have had much better luck raising money than those on the Democratic side.

“What we got are some of these super PACs who’ll spend up to half a billion dollars to try to buy this election, and what I’ve said is we’re not going to unilaterally disarm,” Obama said in an interview Tuesday with WBTV, a CBS affiliate in Charlotte, N.C. “My strong preference would be to completely eliminate the the super PAC process, but we’re not just going to let a whole bunch of folks who are self-interested and aren’t always disclosing what their contributions are, to simply purchase an election.”

Romney has complained about super PAC spending in the GOP primaries, though he has also welcomed support from Restore Our Future and has appeared at several of the group’s events. The Romney campaign said last week that it will also encourage campaign officials to participate in Restore Our Future events following the Obama campaign’s announcement.

The FEC has ruled that candidates can raise money for super PACs, but only within regular federal campaign limits of $2,500 per individual. Leaders from both parties have been lining up to help raise money for super PACs focused on congressional races.