FIRST ON FOX: A group aligned with Senate Majority Leader Chuck Schumer, D-N.Y., has been hit with a complaint alleging they have violated Federal Election Commission (FEC) rules. 

The mysterious entity, called the Last Best Place PAC, recently jumped into the Montana Senate race and began spending millions to target former Navy SEAL Tim Sheehy ahead of the state's Republican primary. 

The Last Best Place PAC is financially driven by Majority Forward, a dark money nonprofit that has put hundreds of thousands toward the Schumer-aligned Senate Majority PAC for salaries, insurance and IT security. Federal records filed last week show Majority Forward funneled $2.14 million to the Last Best Place PAC and was its only funder.

Meanwhile, the group did not file a single independent expenditure report showing those actions, as required by FEC rules, and is now facing a complaint from Americans for Public Trust (APT) over the matter.

SCHUMER-ALIGNED GROUP PULLED IN $270M FROM SECRET DONORS IN RECENT YEARS AS HE DECRIED DARK MONEY

Schumer talks to media

Senate Majority Leader Chuck Schumer, D-N.Y., answers questions from reporters outside the Senate chamber, at the Capitol in Washington, Tuesday, Nov. 28, 2023. President Joe Biden's nearly $106 billion aid package for Ukraine, Israel and other needs is sitting idle in Congress as Republicans are insisting on U.S.-Mexico border policy provisions in exchange for any new U.S. dollars for Ukraine in its fight against Russia.  (AP Photo/J. Scott Applewhite)

"Last Best Place PAC is masquerading as a local Montana operation while quietly laundering millions of dollars from DC liberals," APT executive director Caitlin Sutherland told Fox News Digital. 

"Spending massive sums of money to impact this election without filing the legally required reports flies in the face of the letter and spirit of our election laws," Sutherland continued. "This behavior warrants an immediate investigation by the FEC in order to uphold the basic standards of transparency and public trust."

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Within the complaint filed to the FEC on Monday morning, APT says that the Last Best Place PAC has "made independent expenditures aggregating $10,000 or more in a calendar year," and reporting had indicated as much. Therefore, the Last Best Place PAC was required to submit independent expenditure reports displaying their ad buys but neglected to do so.

Republican Montana Senate candidate and former Navy SEAL Tim Sheehy.

Republican Montana Senate candidate and former Navy SEAL Tim Sheehy. (Tim Sheehy For Montana)

The Last Best Place PAC's recently filed year-end report also shed light on its media expenditures. According to its filing, the PAC poured over $2.1 million into media buys and production costs between early September and late December with Waterfront Strategies and Mountain Media. 

APT's complaint states the committee "is failing to meet the legal requirements and basic standards of transparency to which every other independent expenditure committee is required to adhere" and called on the FEC to immediately investigate and "determine and impose appropriate sanctions for any and all violations."

The most recent attempt to stir up the Montana Republican primary, where Sheehy faces a potential challenge from Rep. Matt Rosendale, R-Mont., is only the latest of Schumer-tied groups receiving criticism for meddling in GOP races.

EMIGRANT, MT - JULY 24: Montana Republican Congressman Matt Rosendale speaks at the ceremony to honor the four airman killed in a 1962 B-47 crash at 8,500 feet on Emigrant Peak on July 24, 2021 in Emigrant, Montana. A recent bipartisan Act of Congress will honor the airman with a memorial at the crash site. (Photo by William Campbell/Getty Images)

EMIGRANT, MT - JULY 24: Montana Republican Congressman Matt Rosendale speaks at the ceremony to honor the four airman killed in a 1962 B-47 crash at 8,500 feet on Emigrant Peak on July 24, 2021 in Emigrant, Montana. A recent bipartisan Act of Congress will honor the airman with a memorial at the crash site. (Photo by William Campbell/Getty Images) (William Campbell)

In the Big Sky State, Last Best Place PAC is reportedly planning to spend over $5 million attacking Sheehy in the race to unseat vulnerable Democrat Sen. Jon Tester, D-Mont., according to AdImpact.

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"The career politicians back in DC are terrified of conservative outsider Tim Sheehy because he’s going to stand shoulder to shoulder with President Trump to drain the swamp, save our country, and put America and Montana First!" Sheehy told Fox News Digital after the Senate Majority PAC confirmed to Fox News Digital they are behind the Last Best Place PAC.

Fox News Digital has reached out to the Senate Majority PAC for comment on the complaint.