An American physicist represented by a team from Norton Rose Fulbright on Monday challenged his identification as a Russian oligarch by the U.S. Treasury Department, arguing Secretary Steven Mnuchin failed to take up a “serious inquiry” before including his name on a list of purported cronies of President Vladimir Putin.

“Instead, the secretary effectively republished the list of Russian billionaires from the March 28, 2017, issue of Forbes Magazine,” lawyers for Dr. Valentin Gapontsev, a Russian-born businessman and U.S. citizen, wrote in their complaint in the U.S. District Court for the District of Columbia. Forbes itself reported in January that the names of Russians appearing on the U.S. Treasury’s list appeared in a 2017 Forbes report on the world’s billionaires.