ExxonMobil Corp sued the US government, blasting as "unlawful" and "capricious" a $2 million fine levied against it for a three-year-old oil joint venture with Russia’s Rosneft.

The US Treasury Department slapped the world’s largest publicly traded oil producer with the fine for "reckless disregard" of US sanctions in dealings with Russia in 2014 when Secretary of State Rex Tillerson was Exxon’s chief executive.

The lawsuit and the Treasury’s unusually detailed statement on Exxon’s conduct represented an extraordinary confrontation between a major American company and the US government, made all the more striking because Exxon’s former CEO is now in President Donald Trump’s Cabinet.

Exxon took the government to court despite the fact that the fine, the maximum allowed, would have a minor impact on the company, which made $7.84 billion in profit last year.

The fine came after a US review of deals Exxon signed with Rosneft, Russia’s largest oil producer, weeks after Washington imposed sanctions on Moscow for annexing Ukraine’s Crimea region.

Between May 14 and May 23, 2014, top US-based Exxon executives signed eight documents with Igor Sechin, the head of state-run Rosneft, the Treasury’s Office of Foreign Assets Control (OFAC) said in the statement on its website.

OFAC said Exxon had "demonstrated reckless disregard for US sanctions requirements" by signing the deals with Sechin just weeks after the US blacklisted him.

The Treasury imposed sanctions on Sechin in April 2014 as part of measures to pressure Russia over its intervention in Ukraine, saying Sechin had shown "utter loyalty" to Russian President Vladimir Putin.

The sanctions prohibit US citizens or people in the US from dealing with those on the blacklist, such as Sechin. Rosneft itself is subject to narrower US sanctions that still allow Americans to deal with the company on some transactions.