Tony Podesta’s lawyer issued a firm warning to Tucker Carlson and Fox News to stop claiming Podesta’s lobbying company, the Podesta Group, colluded with Russia.

“On behalf of Mr. Podesta, I write to demand that you and Fox News Channel immediately cease and desist disseminating false and misleading reports about Mr. Podesta and the Podesta Group,” a letter penned by Geoffrey Garinther states.

Tucker Carlson reported on his Fox News show last week a source told him special counsel Robert Mueller's probe "has broadened to determine which people and organizations in Washington have spent years working secretly as de facto operatives on behalf of the Russia government," and "the Podesta Group is chief among these de facto foreign operatives."

“Your statements are fabricated and demonstrate a callous disregard for the truth,” the letter says in closing.

Podesta announced Monday he would resign from his company in response to Mueller’s investigation, which is trying to determine if the Trump campaign colluded with Russia and also was investigating former Trump campaign chairman Paul Manafort.

Manafort and Podesta’s firms both worked in public relations for the European Centre for a Modern Ukraine, or ECMU, NBC News reported Monday. The organization is suspected to be backed by the pro-Russia political group Party of Regions.

As a result, the Podesta Group gained attention because it may have violated the Foreign Agents Registration Act, or FARA, which states Americans who lobby for foreign governments, leaders, or political parties must make their actions known to the Justice Department. However, both firms only disclosed their activities after media reports of their affiliations with the ECMU.

The Podesta's attorney's letter says Carlson and Fox News relayed false information including that Manafort was seen “once a month” in the Podesta Group’s offices; that Manafort and the Podesta Group worked for the Russian government as a result of Podesta Group’s representation of the ECMU; and that they were a “sham” organization.

The letter also states the Podesta Group complied with FARA and disclosed its representation of the ECMU.

Manafort was indicted by a federal grand jury Monday on 12 charges, along with his associate Rick Gates, as part of Mueller’s investigation to determine if the Trump campaign colluded with Russia during the 2016 election.