The U.S. says Exxon violated the sanctions in May 2014 when two subsidiaries signed deals with Igor Sechin. Sechin is the chairman of Russian oil giant Rosneft and is on a U.S. blacklist over Russia’s actions in Ukraine.

The Treasury Department says Exxon showed “reckless disregard” for sanctions by dealing with a person on that blacklist and that top Exxon executives knew Sechin was blacklisted when they did business with him. The U.S. says Exxon caused “significant harm” to the sanctions program.