Washington: For months, White House hopefuls from both parties have been raising millions in unlimited contributions at upscale fund-raisers from Manhattan to Palm Springs, California — all without officially declaring themselves candidates and becoming subject to federal caps on contributions.

Only a few of some 20 would-be presidential candidates have even bothered to set up the “exploratory” committees that were once a time-tested way to declare interest in the White House — and that set off their own fund-raising restrictions.

But two leading campaign finance groups charged on Tuesday that the spread of these unofficial campaigns in recent months was not only deceptive, but also illegal.

The groups, the non-partisan Campaign Legal Centre and Democracy 21, filed formal complaints with the Federal Election Commission against four undeclared candidates for president: Jeb Bush, Scott Walker and Rick Santorum, all Republicans; and Martin O’Malley, a Democrat. Both organisations favour more restrictive regulations governing how political money is raised and spent.

Among the prospective White House candidates, those four have been particularly aggressive in appearing at fund-raisers, visiting crucial states like Iowa and New Hampshire, hiring staff members and setting up offices, and positioning themselves for a possible bid, Paul S. Ryan, a lawyer for the centre, said in an interview.

Yet they have skirted federal election law that requires candidates who are “testing the waters” for the White House to limit individual contributions to $2,700 and subject themselves to other restrictions, Ryan charged. Instead, news reports show that Bush and other candidates have used super PACs and other groups that can accept unlimited funds to rake in contributions at $100,000-a-head fund-raisers, even while they put off announcing their candidacies, he said.

“These guys aren’t just testing the waters for president,” Ryan said. “They’re soaking wet.”

Allie Brandenburger, a spokeswoman for Bush, said: “We are fully complying with the law in all activities Gov. Bush is engaging in on the political front. If Gov. Bush engages in any ‘testing the waters’ activities, they will be paid for appropriately under the law and reported at the required time.”

A spokeswoman for Walker, Kirsten Kukowski, did not respond directly to the groups’ charge that his early, unofficial campaigning had not complied with federal election law. She said Walker has been using his PAC, Our American Revival, in “talking to Americans about his reform-minded principles” and that “if there are any announcements about his future, he will do it in accordance with the law.”

Lis Smith, a spokeswoman for O’Malley, said: “Our PAC has been fully compliant with the law. This complaint has no merit and we are confident that — whatever the case may be with the other potential candidates — that is what the FEC will find.”

A spokesman for Santorum did not respond to a request for comment. The FEC said it had received the complaints but declined to comment. The issue will be examined by the agency’s lawyers.

Ryan said that beyond the four candidates named on Tuesday, his group planned to file complaints against other candidates who it believed had also violated the limits on early fund-raising.

Sen. Ted Cruz, R-Texas, is the only major candidate to officially declare his candidacy for the White House. Among the other prospective candidates manoeuvring for 2016 runs, Ryan said only four — Sen. Lindsey Graham and Ben Carson, both Republicans; and Democrats Hillary Rodham Clinton and Jim Webb — appeared to have complied with federal restrictions on candidates who are testing the waters.

Ryan said Clinton, the presumed front-runner for the Democratic nomination, appeared to have abided by federal campaign finance law by using personal funds and volunteer staff members to prepare her expected White House run. He said she also appeared to have kept her distance from a political action committee called Ready for Hillary, which is supporting her but appears to be operating independently. He contrasted the group with Right to Rise, a super PAC set up by associates of Bush in support of his possible White House run that has raised money for him.

The rapid evolution and loose rules around candidate-linked “independent” groups were further underscored on Tuesday by the emergence of yet another outside group with ties to Bush. Unlike the Right to Rise super PAC, the new group is organised as a non-profit corporation, meaning that it is not required to disclose any donors.

In theory, the new group is barred by tax rules from devoting itself to helping to elect Bush. But the non-profit was established by Bill Simon, a friend and aide to Bush, in February in Arkansas, according to papers filed with the Arkansas secretary of state, and its name, Right to Rise Policy Solutions, is partly shared by Bush’s super PAC as well as his leadership PAC.

The similarities suggest that the new group, whose existence was reported Tuesday by The Washington Post, may be the first such political non-profit organisation set up to bolster a single potential presidential candidate.

Kenneth Gross, a campaign finance lawyer in Washington who is not involved in Tuesday’s complaints, said it was highly unlikely that the FEC — which has been gridlocked for years on key legal issues by a partisan split — would reach a consensus on whether the early efforts by Bush and others had violated campaign finance law.

But even without a decision by the FEC, Gross said the legal and policy issues raised by the complaint are important in addressing “uncharted waters” in the rising use of super PACs to raise huge sums of money for undeclared White House candidates.

“The best way to kick off your campaign these days,” he said, “is to deny you’re a candidate.”