When the law firm Skadden, Arps, Slate, Meagher & Flom signed on to work for the Ukrainian government in 2012, it understood the bill would be largely picked up by the steel magnate Victor Pinchuk, a Ukrainian billionaire who has since come under scrutiny from the special counsel’s office, according to a new filing the firm submitted to the U.S. Department of Justice.

Skadden revealed its awareness of Pinchuk’s financial involvement in a lengthy filing made Jan. 18 under the Foreign Agents Registration Act that was required as part of a settlement with the Justice Department. Prosecutors had accused the firm of violating lobbying laws by not earlier registering its work.