A conservative group has filed a petition asking federal regulators to prevent self-funded candidates from emulating former New York mayor Mike Bloomberg, who they say used a loophole to make a historically large $18 million contribution to the Democratic National Committee.

Citizens United, the group widely known for its 2010 namesake landmark Supreme Court case that helped pave the way for super PACs, on Wednesday filed a petition with the Federal Election Commission asking federal regulators to create new rules to limit the amount of leftover money that a self-funded federal candidate can transfer to the national party once the candidate has dropped out of the race.

The request followed two FEC complaints filed by other groups that alleged Bloomberg made an improper transfer.

Bloomberg, one of the world’s wealthiest people, was the biggest self-funded candidate in U.S. history. After he suspended his presidential campaign last month, he donated $18 million in leftover campaign cash to the Democratic National Committee. Federal candidates can give unlimited amounts of leftover money to national, state and local political parties as they wind down their campaigns.

Because his campaign was entirely self-funded, this essentially allowed Bloomberg to give far more than the maximum one person can donate to the national party in one year.

Under normal circumstances, federal rules allow individuals to give a maximum of $355,000 per year to the DNC. The party has set up a Democratic Grassroots Victory Fund, a joint fundraising committee with state parties, that allows wealthy individuals to give $865,000 in one year. Bloomberg has already donated the maximum allowed to this account.

In a petition to the FEC, Citizens United and its affiliate Citizens United Foundation asked the agency to close what the groups dubbed the “Bloomberg loophole,” saying that while the transfer “may fall within the letter of the regulation governing transfers of candidate funds to national political party committees it certainly does not fall within the spirit of the law.”

Bloomberg campaign officials and the Democratic National Committee did not respond to requests for comment on Thursday.

David Bossie, president of Citizens United and Citizens United Foundation, said Thursday the groups are seeking to limit the amount of money that can be transferred from a fully self-funded campaign.

Other campaigns accept contributions from donors who adhere to the federal contribution limit of $2,800 per election, while Bloomberg’s account was made up of money donated by the candidate himself, Bossie noted.

“Our proposal is designed to prevent . . . wealthy candidates from evading” that annual contribution limit by running a self-funded presidential campaign, Bossie said.

Bloomberg’s transfer also exposed a potential loophole that could be exploited by bad actors, experts said at the outset of his failed presidential bid.

If someone mounted a self-funded bid solely to evade the individual contribution limit and donate leftover campaign funds to the party, that would be considered a straw donation scheme, experts had said.

Bossie said his complaint also seeks to “prevent phony candidates from evading the limits on direct contributions to national party committees by laundering personal funds through a campaign account.”

Americans for Public Trust, a government oversight nonprofit that launched this year, last week filed an FEC complaint alleging Bloomberg’s donation was in fact a violation of federal campaign finance laws, and that the former mayor “circumvented federal contribution limits” in making the donation.

Great America PAC, which supports President Trump, filed a similar complaint asking the FEC to investigate the transfer.

The FEC is unable to conduct official business because it does not have a voting quorum. A Senate committee last month considered Trump’s nominee to fill a vacancy on the FEC in an effort to restore its operations, but the nomination now remains in limbo as senators respond to the looming economic crisis in the wake of the coronavirus pandemic.

Bloomberg gave more than $935 million of his own money to his three-month White House bid, and his campaign spent at least $510 million of that money.

After suspending his campaign, Bloomberg endorsed former vice president Joe Biden for president and transferred the remaining cash in his presidential campaign account to the DNC. At the time, Bloomberg campaign officials said he wanted to transfer his funds in a way that would “support our eventual nominee and scale the Democratic Party’s general election efforts.”