WASHINGTON – A high-ranking Air Force official said Friday the service would stop launching national security satellites aboard United Launch Alliance’s Atlas 5 rocket if the Treasury Department finds that importing the rocket’s Russian engine violates U.S. sanctions.

Earlier this month, Sen. John McCain (R-Ariz.) asked the Air Force to prove that Russia’s recent reorganization of its space industry does not put ULA’s purchase of RD-180 engines in violation of sanctions the United States imposed against Russian officials in 2014.

U.S. government agencies, led by the Treasury Department, are taking a fresh look at whether RD-180 imports still steer clear of the sanctions.

Lt. Gen. Samuel Greaves, commander of the Air Force’s Space and Missile Systems Center, said the service would abide by Treasury’s findings.

“If we’re not supposed to be flying the RD-180s, they’re grounded,” he said, during a breakfast here hosted by the Air Force Association. “If these folks are on the sanctioned list, if the Department of Treasury comes back and says that there’s a problem with that relationship, then we have to work with the Congress and others to move ahead. We will not violate the law.”

The Air Force relies on ULA’s Atlas 5 rocket to launch a majority of national security satellites. ULA buys the RD-180, the first stage engine for the rocket, from Florida-based RD-AMROSS, a joint venture between Energomash and Pratt and Whitney of Hartford, Connecticut. RD-AMROSS, in turn, buys the engines from NPO Energomash of Khimki, Russia.

The grounding of the Atlas 5 would create a significant obstacle for the Pentagon, where top officials say space is more valuable to their warfighting efforts than at any other time in history.

“We [would] have some decisions to make,” Greaves said.

McCain, the chairman of the Senate Armed Services Committee, used the National Defense Authorization Act of 2016 to impose strict limits on the number of RD-180 engine ULA could order for future Air Force launches. But Sen. Richard Shelby (R-Ala.), wielding his clout on the Senate Appropriations Committee, used a must-pass spending bill to eliminate the RD-180 restrictions that had become law just weeks earlier.

McCain, joined by House Majority Leader Kevin McCarthy (R-Calif.), in late January introduced a standalone bill to reinstate the RD-180 restrictions.

That same week, McCain chaired a military space launch hearing where he called for the Air Force to get a fresh legal opinion on whether RD-18o imports violate sanctions the U.S. imposed on a slew of Russian officials the wake of Russia’s 2014 annexation of Ukraine’s Crimean peninsula.

In a Feb. 10 letter to Air Force Secretary Deborah Lee James and Frank Kendall, the Pentagon’s acquisition czar, McCain singled out two high-ranking Russian officials whose newly given roles overseeing Russia’s state-run space sector warrant a closer look in light of the sanctions.

RD-AMROSS spokesman Bradley Akubuiro told SpaceNews the officials McCain named — Russian Deputy Prime Minister Dmitry Rogozin and Sergei Chemezov, an adviser to Russian President Vladimir Putin — are not members of the RD-AMROSS or NPO Energomash boards, nor do they financially benefit from RD-180 sales.

“With each new sanctions announcement, RD AMROSS works with its supply base, including NPO Energomash, to conduct the proper due diligence to ensure our compliance with the U.S. sanctions regime, and to date have identified no business relationships that implicate the U.S. sanctions regime,” Akubuiro said Feb. 16.

Spurred by a SpaceX lawsuit, federal authorities in 2014 examined the RD-180 purchases for violations of sanctions the United States imposed on dozens of Russian officials following Russia’s conflict with Ukraine.

Then, Treasury and Justice department officials said “to the best of our knowledge, purchases from and payments to NPO Energomash” do not constitute a violation.

But the government is taking another look at the issue following Putin’s Dec. 28 order reorganizing Russia’s space sector. This restructuring included placing the Russian space industry and the space agency Roscosmos under a new state corporation, also named Roscosmos.

“The situation has changed,” McCain wrote Feb. 10 (See full text of McCain’s letter below).

In the near future, wrote McCain, the new Roscosmos is expected to merge with the state-owned United Rocket and Space Corporation. Because URSC owns about 75 percent of Energomash, such a move would make Energomash a subsidiary of Roscosmos, he said.

McCain pointed out that Roscosmos is now chaired by Rogozin; Chemezov is also on the Roscosmos board.

Rogozin and Chemezov were among the first Russian officials President Barack Obama slapped with sanctions during the Crimean crisis. Neither Rogozin nor Chemezov are permitted to enter the United States and any U.S.-based assets they own were frozen.

“In overseeing Russia’s military, including its space and rocket industry and instructing Energomash’s board, Rogozin exercises control over companies like Energomash,” McCain told James and Kendall in his letter. “Like all Russian state corporations, Roscosmos will be governed by a board appointed by Putin from a pool of his closest associated and other government apparatchiks – some of whom the U.S. and the European Union have individually sanctioned.”

Rogozin said in 2014 that anyone who thought he benefited from the sale of the engine was a “moron.”