The nonpartisan Campaign Legal Center filed a complaint Thursday with the Federal Election Commission against a “dark money” group with ties to Republicans.

The “pop-up” super PAC, which has not disclosed its donors, has spent more than $2 million mostly supporting progressive candidates in the final days before closely watched Democratic primaries in Pennsylvania, Nebraska and Texas.

The complaint alleges that Lead Left PAC has violated federal campaign-finance laws by sending money to two newly formed shell companies in order to conceal the recipients of its funds. These companies are likely not the final beneficiaries, according to the complaint, and serve to obscure how the super PAC is actually spending its money.

“It is spending a bunch of money influencing Democratic primaries,” said Saurav Ghosh, the director of federal campaign-finance reform at the Campaign Legal Center. “Our focus is on the spending, because that seems to be essentially the way in which it’s keeping under close guard what its goals are and who’s actually behind the operation.”

Though not explicitly in violation of the law, the Campaign Legal Center complaint also says the organization has “strategically gamed federal reporting deadlines” in order to sidestep disclosing the sources of its funds ahead of the primaries. Nebraska’s primary was Tuesday, Pennsylvania’s primary will take place on May 19 and the Texas runoff is on May 26.

The FEC will almost certainly take no material action on the complaint this month, and it may be many months more — and potentially years — before it does. That’s because the agency has gone more than a year without the required number of commissioners — four — to formalize investigations or penalize campaign-finance scofflaws. Its investigative case backlog is already in the hundreds.

Lead Left PAC did not immediately respond to a request for comment from NOTUS.

The Campaign Legal Center’s complaint notes that Lead Left PAC’s address is a Staples store with a virtual mailbox service. Punchbowl News previously reported that the group has WinRed, the leading Republican fundraising platform, in the metadata of its website.

“It walks like a duck, quacks like a duck, it’s probably a duck,” Ghosh said. “This is a phenomenon that we’ve been observing for several election cycles. Basically, it looks like an effort to influence who gets elected in Democratic primaries because of a perception that they would be a more-easy-to-defeat candidate in the general election.”

More than half of the spending by the mystery super PAC has gone to supporting Lamont McClure, a former county executive, and to opposing other Democratic candidates, particularly Bob Brooks and Ryan Crosswell, in Pennsylvania’s 7th Congressional District’s Democratic primary. The Democratic Congressional Campaign Committee is supporting Brooks.

The Democratic nominee will challenge the Republican incumbent, Rep. Ryan Mackenzie, in one of the most hotly contested races in the country.

Lead Left PAC also successfully opposed John Cavanaugh in Nebraska’s 2nd Congressional District and is backing Maureen Galindo, a sex therapist who has been accused of antisemitism by local officials in both parties, in Texas’ 35th Congressional District.

Ghosh warned that committees like this are becoming more and more common in U.S. election cycles, adding that voters should scrutinize the TV advertisements and mailers they see before taking their contents at face value.

“The effort to meddle in the other party’s primaries, that’s been going on for some years now, and it’s becoming a little more common,” Ghosh said. “The real takeaway for voters is, when you’re seeing an ad, you have to be incredibly skeptical about not only who’s paying for it, but what their motivations are.”