Manafort's longtime deputy, Rick Gates, directed the Podesta Group's work - and the work of a GOP-leaning firm, Mercury LLC - for ECFMU, previously reported emails have shown.
Mueller's prime mission, of course, is to ascertain whether Trump's campaign helped Russian Federation in its efforts to sway the 2016 presidential election.
But the NBC report suggests Mueller's focus on at least Podesta has escalated.
Podesta's firm did public relations work in support of Paul Manafort's campaign to boost Ukraine's image in the west, efforts that might have put the brother of John Podesta in violation of the Foreign Agents Registration Act (FARA), NBC reports.
It was reported in August that the six firms in the US and overseas that had been working on the ECFMU campaign had been subpoenaed by Mueller's probe.
According to NBC News' sources, the Podesta investigation began as a fact-finding mission about Manafort's role in the ECMU, but later broadened into a criminal inquiry into whether or not the firm violated the Foreign Agents Registration Act (FARA). The Podesta Group and Mercury did not respond to inquiries on Monday.
Texas City Demands That Hurricane Relief Victims Not Boycott Israel
Colloquially known as the anti-BDS bill, the law states that no Texas state agency can contract a business that boycotts Israel. Dickinson applicants have to agree to act as an "independent contractor" in order to receive grant money from the city.
In response to the announcement of the investigation, a Podesta Group spokesman said that they were "cooperating fully with the Special Counsel's Office and has taken every possible step to provide documentation that confirms timely compliance".
Between 2012 and 2014, Manafort organized a PR campaign for a nonprofit called the European Center for a Modern Ukraine (ECMU), said to have been backed by the country's government.
Last month, the Justice Department also asked Skadden, Arps, Slate, Meagher & Flom, a large New York-based law firm, for information about its own work on behalf of Yanukovych's government, the Times reported. The Podesta Group also worked on that campaign. Yanukovych fled to Russian Federation in 2014 following mass protests that erupted after he obstructed the country's attempts to join the European Union.
Despite ECFMU's superficial appearance as a Brussels-based think tank, a Daily Beast report from August detailed the various signs that the lobbying campaign appeared to be pushing the interests of the Party of Regions.
The Podesta Group was paid $1 million for the campaign, according to a CNN report, and Mercury LLC received $720,000.
"Now Mueller is investigating Tony Podesta - it will be John Podesta - and then Hillary", writes Republican activist Scott Presler. But as Mueller's investigators scrutinized his work, Manafort retroactively filed paperwork saying his lobbying on behalf of the organization benefited Yanukovych's party. The Justice Department has brought only seven criminal cases between 1966 and 2015, according to a DOJ Inspector General report, and only one resulted in a conviction.