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.
When Tillerson was CEO, he said Exxon didn't support sanctions generally because it found them usually ineffective.