An attorney for a prominent law firm is pleading guilty to lying to federal authorities about his interactions with a former Trump campaign associate.

Alex van der Zwaan is entering the plea in federal court in Washington where he is admitting to lying to special counsel Robert Mueller's investigators about his interactions with Rick Gates. Gates is a former aide on U.S. President Donald Trump's campaign and a longtime associate of former Trump campaign chairman Paul Manafort.

The charge against van der Zwaan does not involve election meddling or the Trump campaign's operations. It stems from the special counsel's investigation into a covert Washington lobbying campaign Manafort and Gates are accused of directing on behalf of pro-Russian Ukrainian interests.

Manafort and Gates have pleaded not guilty.

The law firm where van der Zwaan worked says it fired him last year and has been co-operating with authorities.

Skadden, Arps, Slate, Meagher & Flom LLP issued a statement Tuesday after news broke that van der Zwaan had been charged.