WASHINGTON — The $ 2 million fine that the Treasury Department levied on Exxon Mobil this week for violating sanctions against Russia is just a sliver of the oil company’s $ 7.8 billion in profit last year. But Exxon has decided nonetheless to wage a legal battle — one that could make President Trump’s cabinet meetings decidedly awkward.
Rex W. Tillerson, now the secretary of state, was Exxon’s chief executive at the time of the actions in dispute in 2014. And his former company is suing the Treasury and Steven Mnuchin, the Treasury secretary, in hopes of getting the penalty withdrawn and its reputation cleared.
The clash has created a new wrinkle in the intrigue that has captivated Mr. Trump’s Washington, and it has left some wondering why Exxon would fight over a paltry sum as a political furor over Russia swirls.
“It’s a fascinating dynamic playing itself out,” said Peter Kucik, a former official in Treasury Department’s Office of Foreign Assets Control. “It would be difficult to script this.”
The rationale for the lawsuit appears to go beyond the financial impact of the fine. Exxon feels that its reputation is at stake and that the threat of more sanctions, potentially costlier, is looming.
Treasury and Exxon have been sparring for years over the company’s ability to do business with Russia. The Trump administration has recently been trying to show its mettle with a flurry of sanctions announcements amid concerns that Mr. Trump may soften those already enacted. At the same time, a Republican-controlled Congress is threatening to increase Russia sanctions, which could cost the energy industry billions of dollars.
The core of the dispute is whether Exxon violated sanctions by signing eight contracts with Rosneft, the Russian state oil company, in May 2014. Signing on behalf of the Russian state oil company was Igor Sechin, its chief executive, who had been blacklisted by Treasury a month before.
Exxon argues that it had received guidance that it was not a problem if Mr. Sechin signed such contracts in his official capacity, as long as the company was not doing business with him as an individual. Exxon points to briefings by White House officials and news articles, including one from The New York Times that year, giving the impression that the company was in the clear.
“U.S. persons are not prohibited from dealing with Rosneft, including participating in meetings of the company board,” a Treasury official told The Times in April 2014.
Exxon and the Treasury Department discussed the situation directly in 2015, but according to Exxon it heard nothing more for a year. Then last year, Treasury indicated that the comments made by White House and Treasury officials in the press did not give Exxon the go-ahead. Instead, the department pointed to guidance on its website that warned companies to be cautious about entering into contracts with people who were under sanction.
Believing that it had followed the guidance it was given, Exxon declined to concede it had violated the sanctions and submit to a penalty.
“The issue is will the U.S. Department of Justice defend a position by an agency that you shouldn’t listen to what the White House says?” said Alan T. Jeffers, an Exxon spokesman. “We feel very strongly that what they’ve chosen to do is contrary to the law.”
For its part, the Treasury Department has been silent on the matter beyond a three-page enforcement document issued on Thursday stating that Exxon’s “senior-most executives” knew of Mr. Sechin’s status when Exxon engaged in behavior that caused “significant harm” to the sanctions program.
The department would not say if Mr. Mnuchin was involved in the final decision, and Mr. Tillerson’s aides maintain that he was unaware because he had recused himself from matters related to Exxon.
“You have to wonder how far up the chain at the Treasury Department this went,” said Thad McBride, an international trade lawyer at Bass, Berry & Sims, noting that the pointed language about high-level knowledge appeared to be directed at Mr. Tillerson. “It is extremely unusual that Treasury would do that.”
The State and Treasury Departments typically coordinate closely on sanctions. At the State Department, an Office of Economic Sanctions Policy advises Treasury officials on foreign policy. The agencies often announce new sanctions in tandem.
Sanctions experts said on Friday that the broad interpretation that Treasury offered on sanctions could jeopardize many other deals that companies do with Rosneft, and that the scope of the ruling was probably what prompted Exxon to fight back with such ferocity.
Scott M. Flicker, a lawyer at the firm Paul Hastings specializing in trade sanctions, said the penalty would have consequences for any American company that does business with Rosneft or might be considering doing so.
“How do you propose that Exxon deal with Rosneft?” Mr. Flicker said. “Is Rosneft supposed to fire their C.E.O.?”
Exxon has projects in Russia that are allowed under American sanctions, and others, worth billions of dollars, that can go ahead only if sanctions are lifted.
In its most valuable contract in the country, Exxon won a coveted deal to drill for oil in the Russian sector of the Arctic Ocean and offshore in the Black Sea after BP was forced out in a lawsuit filed by Russian oligarchs.
The Russian government has optimistically called the agreement a $ 500 billion deal.
In its early phases, the agreement mostly called for Exxon to make investments in Russia, and the company sank about $ 700 million drilling an exploration well in the Kara Sea, said to be the northernmost oil well ever drilled.
Sanctions that limit lending with Rosneft to short-term loans rule out further Exxon investment. The sanctions also prohibit transfers of shale oil and Arctic offshore drilling technology.
Rosneft has not canceled the contract, meaning that it could be resumed if sanctions are lifted, opening vast new drilling areas for Exxon in the thawing Arctic above Russia.
Separately, Exxon and Rosneft have a production-sharing deal to pump oil on Sakhalin Island, off the east coast of Siberia, that was not affected by sanctions.
To the chagrin of Exxon and other American energy companies, tougher sanctions could be on the way in response to Russian meddling in the 2016 election.
Legislation stalled in Congress would bar American companies from pursuing joint energy projects anywhere in the world with Russian companies that are under sanctions. While the White House has resisted the measure, it has bipartisan support and could cost energy companies billions of dollars.
The tangle between Exxon and the government has also raised concern within the industry.
“The industry understands the use of targeted sanctions on foreign entities for national security purposes, but when the U.S. government imposes prohibitions, they must provide clear guidance that enables companies to comply,” said Megan Bloomgren, a spokeswoman for the American Petroleum Institute, a lobbying group. “Consistency and predictability are important to avoid a chilling effect on investment.”