High-powered Democratic lobbyist Tony Podesta and the Podesta Group are subjects of a criminal investigation led by Special Counsel Robert Mueller, according to a new report.

Mueller is looking into Podesta and his lobbying firm for potentially violating a federal disclosure law—called the Foreign Agents Registration Act—for groups who work on behalf of foreign governments, NBC News reports. The lobbyist has been influential in Democratic politics for years, and his brother, John, was chairman of Hillary Clinton's 2016 presidential campaign.

Mueller is leading the federal investigation into allegations of collusion between President Donald Trump's campaign and the Kremlin in the 2016 election. The investigation into Podesta stemmed from a probe into former Trump campaign manager Paul Manafort's finances.

According to NBC News sources, the Podesta Group was one of several firms to work on Manafort's public relations campaign for the European Centre for a Modern Ukraine:

The sources said the investigation into Podesta and his company began as more of a fact-finding mission about the ECMU and Manafort's role in the campaign, but has now morphed into a criminal inquiry into whether the firm violated the Foreign Agents Registration Act, known as FARA. Under FARA, people who lobby on behalf of foreign governments, leaders or political parties must file detailed disclosures about their spending and activities with the Justice Department. Willful failure to file the forms is a felony and can result in up to five years in prison, though such prosecutions are rare. The Podesta Group filed a FARA registration for its work with ECMU only after the payments were reported by the media. Manafort's firm also filed a FARA registration after media reports in June disclosed its work in Ukraine from 2012 through 2014. The ECMU was reportedly backed by the Party of Regions, the pro-Russian and oligarch-funded Ukrainian political party for which Manafort worked as a consultant, and which paid his firm millions. Viktor Yanukovych of the Party of Regions, a Manafort client, was president of Ukraine during the ECMU campaign, which ran from 2012 to 2014. He fled the country in 2014.

The Podesta Group said in a statement that the firm "is cooperating fully with the Special Counsel's office and has taken every possible step to provide documentation that confirms timely compliance. In all of our client engagements, the Podesta Group conducts due diligence and consults with appropriate legal experts to ensure compliance with disclosure regulations at all times — and we did so in this case."

The Free Beacon reported last year on Tony Podesta failing to file legally required disclosures for his advocacy on behalf of a foreign government in discussions with his brother.

Tony emailed John in January of 2015 wondering if he would attend a meeting with the Indian ambassador to the United States. At the time, the Podesta Group was making $60,000 a month for its work on behalf of the Republic of India:

Tony Podesta sent his email regarding the Indian ambassador on Jan. 1, 2015. The Podesta Group's Foreign Agent Registration Act disclosures list no contact with John Podesta on behalf of a foreign government client in either the second half of 2014 or the first half of 2015. The latter supplemental does disclose contacts with other government officials on the Indian government's behalf, including dozens of congressional offices and officials at the White House National Security Council, State Department, Commerce Department, and the office of the U.S. Trade Representative.

The Podesta Group later admitted the previously undisclosed advocacy in paperwork received three days after Clinton lost to Trump in the 2016 election.

NBC News reported John Podesta is no longer affiliated with the Podesta Group and is not part of Mueller's investigation.