The Department of Defense’s Inspector General has launched an investigation into accusations by a top United Launch Alliance executive that Senator John McCain was working with Elon Musk to outlaw a Russian rocket engine that he views as his company’s competition.

Last week, ULA Engineering Vice President Brett Tobey resigned after it became public that he had accused McCain of teaming up with the SpaceX founder to ban the imported RD-180 engine that is used to power ULA’s Atlas V launch vehicles. ULA, a collaboration of Boeing and Lockheed Martin, and SpaceX are competing for Pentagon business following the certification of the SpaceX Falcon 9 rocket for military space launches.

"At the request of the Secretary of Defense, the OIG DoD has opened an investigation regarding assertions made by United Launch Alliance’s (ULA) former Vice-President of Engineering relating to competition for national security space launch and whether contracts to ULA were awarded in accordance with DoD and Federal regulations," according to a March 22 DoD IG memo to the Air Force secretary. "This investigation will include, but is not limited to, site visits, interviews, and documentation review with DoD and ULA personnel."

Audio obtained by Space News captured Tobey making the accusations during a presentation in mid-March at the University of Colorado.

“This guy right here, John McCain, who basically doesn’t like us; he’s like this with Elon Musk,” Tobey said during a March 15 presentation at the University of Colorado-Boulder, according to audio posted by Space News. “So Elon Musk says, 'Why don’t you guys go, why don’t you go after United Launch Alliance and see if you can get that engine to be outlawed?' ”

During his speech, Tobey suggested “silencing” McCain, who is the Senate Armed Services Committee chairman.

“The problem is that it carries a $1 billion or $2 billion budget, and is it worth that billion or two dollars of taxpayer money just to silence John McCain, who’s the squeaky wheel in all this?” Tobey said. “It really is a one-man band out there that’s driving forward. Everyone wants to get off of the RD-180 engine, but they want to do it in a more logical and organized way that basically doesn’t put those national assets at risk.”

ULA CEO Tony Bruno did not approve of Tobey’s commentary however, announcing that his employee had resigned, effective immediately, and claiming that his company welcomes competition.

“The views, positions and inaccurate statements Mr. Tobey presented at his recent speaking engagement were not aligned with the direction of the company, my views, nor the views I expect from ULA leaders,” Bruno said in a statement. “Mr. Tobey resigned his position at ULA effective immediately.”

Following the reports, Defense Secretary Ashton Carter called the statements “concerning” and called for “appropriate action” from the Pentagon Inspector General, Pentagon spokesman Peter Cook said in a statement to Defense News.

"The Department strives to ensure all contracts are awarded in a fair and impartial manner based strictly on the terms of the solicitation and source selection criteria," Cook said in a March 18 email. "The Secretary is concerned by recent statements regarding competition for national security space launch and, consistent with the recommendation of Frank Kendall, Under Secretary of Defense for Acquisition, Technology and Logistics, and Deborah James, Secretary of the Air Force, has referred the matter to the DoD Inspector General for appropriate action."

McCain has reportedly sought a ban on the RD-180 engine because of what he has called “Russian aggression” in the Middle East and Eastern Europe. Other lawmakers have pushed to allow the continued purchase of the Russian rocket until a domestic alternative becomes available.

"These statements raised troubling questions about the nature of the relationship between the Department of Defense and ULA," McCain said in a statement. "This committee treats with the utmost seriousness any implication that the department showed favoritism to a major defense contractor or that efforts have been made to silence members of Congress. Mr. Secretary, I expect that you will make a full investigation into these statements and take action wherever appropriate."