Special counsel Robert Mueller has enlisted agents from the IRS’ Criminal Investigations Unit for his sprawling investigation into Russia’s interference in the 2016 election, the Daily Beast reported late Thursday.

Agents in that specialized unit focus specifically on financial crimes like tax evasion and money laundering, and have worked on previous cases with both Mueller and one of his colleagues on the probe, federal prosecutor Andrew Weissman, according to the Daily Beast.

A spokesman for the special counsel’s office declined the publication’s request for comment.

Possible financial crimes are a primary focus of Mueller’s team of investigators, who are digging through the financial dealings and real estate holdings of a number of President Donald Trump’s associates. Politico reported this week that Mueller was collaborating with New York Attorney General Eric Schneiderman on a probe into the finances of former Trump campaign chairman Paul Manafort.

Trump and his outside legal team have argued that the probe should focus strictly on Russia’s doings, and that past business transactions not related to Russia are out of bounds. But former federal prosecutors told TPM that reviewing the business histories of Trump and his associates would be a basic part of any serious investigation, and key to determining whether Russian operatives had leverage over any of them.

The memo appointing Mueller as special counsel gives him a broad mandate to investigate “any matters” that arise from the probe into Russia’s meddling.

The IRS, of course, has access to Trump’s tax records, which he refused to release during the campaign.

The Trump administration could face some serious roadblocks should Mueller decide he wants to bring charges against Trump associates for violating tax law, according to the Daily Beast. Mueller would need to request approval from the Justice Department’s tax division to pursue those charges, and the President has yet to nominate anyone to run it.