A U.S. appeals court on Tuesday rejected a challenge brought by an associate of Roger Stone, the indicted long-time adviser to President Donald Trump, to the legality of Robert Mueller's 2017 appointment by the Justice Department as special counsel heading the Russia investigation.

In doing so, the U.S. Court of Appeals for the District of Columbia Circuit upheld a lower court's decision to hold Andrew Miller in contempt for refusing to comply with a grand jury subpoena served on him by Mueller, who is investigating potential conspiracy between Trump's 2016 campaign and Moscow.

Miller's case marked the third legal challenge to Mueller's authority that has failed so far, including efforts by Paul Manafort, Trump's former campaign chairman who has been convicted on a series of charges and pleaded guilty to others, and a Russian company accused of meddling in the election.