The Treasury Department on Thursday fined Exxon Mobil Corp. $2 million for violating sanctions against Russia while now-Secretary of State Rex Tillerson was CEO of the company.

According to an enforcement filing from Treasury’s Office of Foreign Assets Control (OFAC), Exxon in 2014 signed “eight legal documents related to oil and gas projects in Russia” with Igor Sechin, the president of Rosneft, a Moscow-owned oil company. Sechin was the subject of U.S. sanctions on Russia following its incursion into Crimea.

Exxon is challenging the fine in court, saying previous government statements about the Russia sanctions implied they would be able to to work with Rosneft.

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Former President Barack Obama Barack Hussein ObamaDemocratic Senate campaign arm outraises GOP by M in August A federal court may have declared immigration arrests unconstitutional Blunt says vote on Trump court nominee different than 2016 because White House, Senate in 'political agreement' MORE signed an executive order establishing sanctions on Russia on March 16, 2014. The Treasury Department added Sechin to the list of people subject to those sanctions that April.

But, according to Treasury, "despite these prohibitions and ExxonMobil's global market and sophistication, ExxonMobil moved forward with signing the legal documents with designated person Igor Sechin between on or about May 14, 2014 and on or about May 23, 2014.”

Exxon called the decision “fundamentally unfair,” and pointed to public comments and fact sheets from the Obama White House that said the sanctions applied only to the personal business interests of people covered by them.

Exxon contends its was allowed to sign a contract with Rosneft because officials believed the sanctions only applied to Sechin’s personal business, and not on his role at the company.

The oil giant challenged the sanctions violation in federal court on Thursday, arguing OFAC “seeks to retroactively enforce a new interpretation of an executive order that is inconsistent with the explicit and unambiguous guidance from the White House and Treasury issued before the relevant conduct and still publicly available today.”

Treasury’s enforcement action said that the executive order, its guidance for companies and the administration’s public statements “all clearly put ExxonMobil on notice that OFAC would consider executing documents with [people subject to sanctions] to violate the prohibitions in the Ukraine-Related Sanctions Regulations.”

Tillerson, now President Trump’s secretary of State, was CEO of Exxon until his retirement from the company in January. He has recused himself from State Department actions related to his former company.

A $2 million fine is the maximum civil penalty for the violations, according to Treasury. It’s also a small fine for Exxon Mobil, whose profits were $7.8 billion in 2016.

—Updated at 3:35 p.m.