WASHINGTON – U.S. Sen. John McCain (R-Ariz.) said he would consider an “unrestricted prohibition” on the Russian rocket engine that powers United Launch Alliance’s Atlas 5 rocket following the company’s decision not to bid on the Defense Department’s first competitive launch contract in a decade.

In a Dec. 8 letter to U.S. Defense Secretary Ashton Carter, McCain, who chairs the Senate Armed Services Committee, also requested an audit of ULA’s accounting systems and a report on whether the company tried to “subvert” Congress by assigning non-military missions to its controversial Atlas 5 rocket, which is powered by the Russian-built RD-180 engine.

Both requests relate to ULA’s explanation of why it did not bid to launch a GPS 3 satellite in 2018, effectively ceding the contract to rival SpaceX of Hawthorne, California. McCain said he was “troubled” by ULA’s explanation, which cited the congressionally imposed ban on future use of Russian engines for military launches and issues related to the structure of the procurement.

Specifically, ULA said it did not have an engine available for the mission in question, nor did it have the accounting systems to certify that its existing Air Force business would not benefit its bid, as the procurement required. In addition, ULA said the Air Force’s selection criteria gave little weight to past performance and reliablity, two of the company’s strengths.

“These tactics are inappropriate and intended to support an effort in the Congress to subvert the authorization process,” McCain said. The recently passed National Defense Authorization Act for Fiscal Year 2016, drafted in part by McCain’s committee, exempted four engines from the ban for future competitions, but ULA is seeking much broader relief.

Jessica Rye, a spokeswoman for Denver-based ULA, declined to comment.

In the letter, McCain said he found ULA’s claim that it did not have an engine available for the competition “especially dubious.”

The National Defense Authorization Act for 2015, which imposed the Russian engine ban, exempted five engines the company already had in possession to enable ULA to compete for national security launches. But in early October, shortly after the Air Force issued a request for bids on the GPS launch, ULA said those engines had been allocated to nonmilitary missions, which are not covered by the ban.

“Instead of setting those engines aside for national security launches, ULA rushed to assign them to non-national security launches that are unrestricted in their use of Russian engines,” McCain wrote.

McCain asked the Defense Department to report on “when ULA first began assigning rockets to specific launches and when it first started to reassign launches to prevent the use of RD-180s that were originally available for competitive launches.” The senator also asked Carter to work with the NASA administrator to determine “whether ULA’s reassigning those engines was early-to-need and if ULA could have procured other engines in time to meet actual launch dates.”

Finally, McCain said he was worried that ULA accounting system could undermine future Air Force launch competitions. The GPS 3 mission is the first of nine medium-class launches the Air Force intends to put out for bid by the end of 2017. Of the nine, six are for GPS 3 satellites.

ULA has said modifying its accounting system would throw it out of compliance with those existing contracts. The Air Force requires certification that ULA’s other Air Force business does not benefit its bids.

Each year, the Air Force pays ULA about $800 million to $1 billion to help cover overhead costs and services not necessarily associated with a given launch. This contract has been branded as a subsidy by ULA’s competitors.

“ULA asserts it is unable to differentiate such costs sufficiently in order to submit a compliant proposal,” McCain wrote. “It would also suggest that ULA will not be able to compete for any future launch that would require an ‘apples-to-apples’ comparison between the highly-subsidized incumbent and unsubsidized new entrants.”

McCain’s letter did not elaborate on his plan to broaden the ban on Russian-made engine technology. Banning the use of the RD-180 for NASA missions, for example, likely would require a legislation that typically falls under the jurisdiction of different congressional committee.