The U.S. Justice Department has reportedly launched an investigation into Blue Star Strategies, a consulting firm linked to President Joe Biden’s son, for potential illegal lobbying.

Hunter Biden sat on the board of Burisma, the Ukrainian energy company that was one of Blue Star’s clients. According to Politico, the Delaware U.S. Attorney’s Office is involved in the probe, as are lawyers in the National Security Division at the Justice Department’s Washington headquarters. The Delaware office is also investigating Hunter Biden for potential tax violations, the news outlet said.

Blue Star Strategies is a Washington lobbying and public affairs firm that also has offices in Brussels, Buenos Aires, Paris and Vienna.

The reported probe comes as Hunter Biden, who served on the board of Burisma from 2014 to 2019, has denied any wrongdoing with his work for the energy company, despite claims from former President Donald Trump and his allies there was a conflict of interest with his father serving as vice president in the Barack Obama administration.

Hunter Biden has denied using his influence with his father to aid Burisma. But Republicans coming to Trump’s defense after last year’s impeachment trial have encouraged investigations of Hunter Biden’s activities.

Much of the Justice Department’s previous probes were focused on foreign governments’ efforts to influence U.S. politics through covert lobbying operations, Politico said. Much of that enforcement work has focused on Republicans linked to Trump, including an active probe of his personal lawyer Rudy Giuliani.

Giuliani, a Republican and former mayor of New York City, has not been charged with a crime. He has said all of his activities in Ukraine were conducted on Trump’s behalf. At the time, Giuliani was leading a campaign to press Ukraine for an investigation into Joe Biden and his son, Hunter, before Biden was elected president.

This latest Justice Department effort is an indication that firms associated with the Democratic Party may also begin receiving a heightened focus.