Newly released tax documents showing a plunge in Clinton Foundation donations after Hillary Clinton’s 2016 presidential election defeat have fueled long-standing Republican allegations of possible “pay-to-play” transactions at the organization, amid a Justice Department probe covering foundation issues.

The tax filings, which were made public this month, show the Clinton Foundation pulled in $62.9 million in 2016, but only $26.6 million the following year, representing a nearly 58 percent drop. Tax documents for 2018 are not yet available.

A spokesman for the foundation told The New York Post, which first reported the figures, that they “anticipated a decline” in 2017 and said it was “largely attributable to the absence of sponsorship and membership contributions for CGI [Clinton Global Initiative].”

The final CGI meeting was held in 2016, and the wind-down was a likely factor in the donation drop. Representatives for the Clinton Foundation did not immediately respond to Fox News’ request for comment.

But the filings further emboldened congressional Republicans concerned the foundation benefited first from Clinton's position atop the State Department and later as a presidential candidate, by way of donors seeking political favors -- only for that cash flow to dry up when it was clear Hillary Clinton was out of government.

"The remarkable significance of the drop in Clinton foundation donations raises grave concerns their operations were not above board as the American people have been led to believe," House Freedom Caucus Chairman Rep. Mark Meadows, R-N.C., said in a statement to Fox News. "Whenever we look at the possibility of 'pay to play' by government officials, current or former, it demands answers--and anyone who uses public office to sell access for their own financial benefit must be held accountable."

President Trump, citing reports about the foundation's fundraising, tweeted Sunday that it "shows that they illegally played the power game" and "monetized their political influence through the Foundation."

The foundation repeatedly has denied the allegations. The organization, which receives a high four-star rating from Charity Navigator, has a wide-ranging mission to “improve global health and wellness, increase opportunity for women and girls, reduce childhood obesity, and help communities” and more.

But former Attorney General Jeff Sessions, who was fired almost immediately after the midterm elections, revealed in March that he had appointed U.S. Attorney John Huber to lead an evaluation into a range of Clinton-related issues -- including the FBI's handling of the email case as well as the foundation's operations.

Huber has been mum on the investigation since the start, but House Republicans last week announced they plan to hold a hearing on Dec. 5 to hear Huber’s testimony—just one month before Democrats take control of the House.

Rep. Meadows, who heads the House Oversight and Government Reform Subcommittee on Government Operations, told The Hill last week that it was time to “circle back” with Huber on developments in the probe.

“Mr. Huber with the Department of Justice and the FBI has been having an investigation—at least part of his task was to look at the Clinton Foundation and what may or may not have happened as it relates to improper activity with that charitable foundation, so we’ve set a hearing date for December 5th,” Meadows said.

When appointed, Sessions said that Huber was conducting his work “from outside the Washington D.C. area” and would cooperate with Justice Department Inspector General Michael Horowitz. Sessions said, at the time, that Huber’s review would “include a full, complete and objective evaluation of these matters in a manner that is consistent with the law and facts.”

Huber is the twice Senate-confirmed U.S. attorney for the district of Utah. He previously served in leadership roles within the U.S. Attorney’s Office as national security section chief and executive assistant U.S. attorney.

It is noteworthy that the new acting attorney general is Matthew Whitaker, who before joining the Justice Department led The Foundation for Accountability and Civic Trust, a conservative nonprofit that focused heavily on scrutinizing Clinton.

Whitaker, while leading FACT, appeared in more than 200 television and radio appearances from 2014 to September 2017 when he became chief of staff for Sessions. According to The Washington Post, Whitaker criticized Clinton, the Clinton Foundation, the investigation into her private email server and Special Counsel Robert Mueller’s investigation during those appearances more than 700 times.

For statements like these, Whitaker has been criticized by Democrats since assuming his acting post at the Justice Department. Eighteen state attorneys general called for him to recuse himself from overseeing the Russia probe.

Earlier this month, the Justice Department Office of Legal Counsel issued an opinion supporting Trump’s appointment of Whitaker.

The scrutiny of the Clinton Foundation, however, will likely continue to be overshadowed by the expected conclusion of Mueller's investigation into Russian meddling and potential collusion with Trump campaign associates during the 2016 presidential election.

Trump continues to deny any such collusion, while suggesting as recently as Monday that Democratic figures should face similar scrutiny.

“When Mueller does his final report, will he be covering all of his conflicts of interest in a preamble, will he be recommending action on all of the crimes of many kinds from those ‘on the other side’ (whatever happened to Podesta?), and will he be putting in statements from hundreds of people closely involved with my campaign who never met, saw or spoke to a Russian during this period?” Trump tweeted Monday.

He added: “So many campaign workers, people inside from the beginning, ask me why they have not been called (they want to be). There was NO Collusion & Mueller knows it!”

Fox News’ Jake Gibson and Adam Shaw contributed to this report.