However geopolitical tensions haven’t stopped top defense and intelligence officials from pleading with Congress to allow U.S. aerospace companies to purchase more of the engines, regardless of sanctions against Russia put in place last year.

In a letter to Congress members dated May 11 and made public this week, U.S. Secretary of Defense Ash Carter and Director of National Intelligence James Clapper asked lawmakers to amend federal law to help the Pentagon maintain its guaranteed access to space. The officials say the Russian-made rockets are necessary in order to send U.S. technology into space.

For both Carter and Clapper, assured space access is a matter of national security. It’s also a matter of billions of dollars in contracts for United Launch Alliance (a Boeing-Lockheed Martin venture that has a monopoly on U.S. military space launches) and potentially big business for Elon Musk’s SpaceX, which hopes to begin vying for those same contracts this year.

In a rebuke to Carter and Clapper’s letter, Sen. John McCain remained firm over a provision in last year’s national defense bill concerning trade with Russia —known as Section 1608— that calls for stopping all new purchases of Russian rocket technology sooner rather than later. “What Section 1608 does is prevent over $300 million of precious U.S. defense resources from subsidizing Vladimir Putin and the Russian military industrial base,” he said.

But, for the industry, the real issue is exactly how many of the already ordered RD-180s will United Launch Alliance (ULA) be able to use going forward. If Section 1608 remains unchanged, federal law would only allow ULA to use five Russian engines the company has already paid for. Some government and industry officials want the clause clarified to allow ULA to use up to 18 RD-180s that were already ordered, but not paid for before Russo-American relations took a nosedive.

What lawmakers decide will have a major impact not only on the Pentagon but also U.S. firms ULA and SpaceX. ULA’s Atlas V and Delta IV rockets are currently the only launch vehicles certified for national security-related launches by the U.S. Air Force and require Russian engines to operate.

ULA is currently working on alternative plans involving a new rocket, called Vulcan, that will be powered by made-in-the-USA engines developed by Aerojet-Rocketdyne and Amazon.com founder Jeff Bezos’ Blue Origin, but won’t be finished and certified until 2022 or 2023 at the earliest. Without ULA’s vehicles the Air Force faces “a multi-year gap where we have neither assured access to space nor an environment where price-based competition is possible,” according to the letter submitted by Carter and Clapper.

ULA’s engine shortage means SpaceX may become the sole launch provider for the Air Force after 2018, Air Force Secretary Deborah James said last month at a committee meeting. SpaceX’s Falcon 9 rocket is expected to be approved by the U.S. Air Force for some military launches by the end of June, paving the way for the company’s much larger Falcon Heavy to receive the same certification once the company finishes developing the vehicle (first flight is scheduled for later this year).

Amending Section 1608 would allow ULA to compete against SpaceX for 18 of 34 launches between 2015 and 2022, worth hundreds of millions each. Unfortunately, without a reinterpretation of the law ULA could only work on just five launches before it ran out of rocket cores.

The House Armed Services Committee holds the same views on Russian rockets as both Carter and Clapper and is pushing for changes to the 2016 bill currently making its way through Congress that allow for more Russian engines. However, hawks like McCain—who chairs the Senate Armed Services Committee marking up its version of the 2016 defense authorization bill—remain adamant the U.S. cease using the RD-180 as soon as possible, which leaves the future of U.S. space launches in limbo.