Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

WASHINGTON — The lobbying firms the Podesta Group and Mercury Public Affairs are the unnamed companies in the grand jury indictment of former Trump campaign chairman Paul Manafort and his deputy, Rick Gates, according to three sources with knowledge of the investigation.

The indictment, unsealed Monday, refers to "Company A" and "Company B" as the firms Manafort and Gates solicited in 2012 to lobby on behalf of the Ukranian government. Company A is Mercury Public Affairs and Company B is the Podesta Group, the sources said.

The revelation of the companies’ identities points to more details about the players involved in the high-stakes venture run by Manafort and Gates to push the interest of a pro-Russia Ukranian political party inside the United States. It also provides a glimpse into the material special counsel Robert Mueller has corroborated on both companies and the potential legal repercussions both groups could face.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Tony Podesta, who founded the left-leaning Podesta Group in 1988, stepped down from his position with the firm on Monday morning, an employee told NBC News.

NBC News reported last week that Podesta and the Podesta group had become a subject of Mueller’s probe into ties between the Trump presidential campaign and Russia.

Tony Podesta is the brother of Hillary Clinton campaign chairman John Podesta, who is not under investigation.

The Podesta Group previously withheld from disclosing its work under the Foreign Agents Registrant Act (FARA), claiming they believed the group was not affiliated with the Ukrainian government.

According to the indictment, the lobbying firms were paid $2 million from offshore accounts controlled by Manafort.

Their work included lobbying "multiple members of Congress and their staffs about Ukraine sanctions, the validity of Ukraine elections" that the reasons for imprisoning Yulia Tymoshenko, the political rival of Russian-backed Ukrainian President Viktor Yanukovych.

The indictment also revealed that Gates told Company A, now known to be Mercury, in February 2012 that it would be "representing the Government of Ukraine in [Washington] D.C."

A spokeswoman for Mercury could not be reached for comment. A spokeswoman for the Podesta Group declined to comment.

Manafort and Gates attempted to distance themselves from the work of the lobbying firms after press reports in August 2016, according to the indictment.