WASHINGTON –  U.S. Sen. John McCain (R-Ariz.) has asked the chairman of the Senate Appropriations Committee, Sen. Thad Cochran (R-Miss.), to reject the idea of inserting a provision into a must-pass federal spending bill that would give the U.S. military access to a controversial Russian rocket engine until an alternative becomes available.

The provision, if approved, would effectively neutralize the Russian engine ban imposed by Congress following Russia’s incursion into Ukraine in 2014. Government launch services provider United Launch Alliance, whose workhorse Atlas 5 rocket is powered by the Russian-built RD-180 engine, has said the ban will leave it unable to compete for future U.S. military business against newcomer SpaceX.

McCain, who chairs the Senate Armed Services Committee, supported a provision in the National Defense Authorization Act of 2016, now awaiting the president’s signature, that gives ULA access to four more RD-180s for upcoming competitions, a number the company says is not nearly enough to keep it in the military launch business until it can field a new rocket around 2021. The House version of that bill would have granted ULA access to nine more engines, but the Senate position prevailed.

Now, however, Sen. Richard Shelby (R-Ala.), a senior member of the Senate Appropriations Committee, is considering adding language to a spending bill that would give the Air Force access to the RD-180 until an alternative becomes available, his office has said. The Defense Department, like the rest of the federal government, is currently funded under a continuing resolution that expires Dec. 11, and a new bill must be passed to avoid a government shutdown.

ULA builds the Atlas 5 at its factory in Decatur, Alabama.

In a Nov. 19 letter,  McCain asked Cochran to “respect the well-informed work my committee took” and to avoid the “year-over-year relitigation” of the engine issue.

“Recent attempts by the incumbent contractor to manufacture a crisis by prematurely diminishing its stockpile of engines purchased prior to the Russian invasion of Crimea should be viewed with skepticism and scrutinized heavily,” McCain wrote in the letter, a copy of which was obtained by SpaceNews. “Such efforts should not be misconstrued as a compelling reason to undermine any sanctions on Russia while they occupy Crimea, destabilize Ukraine, bolster Assad in Syria, send weapons to Iran and violate the 1987 Intermediate Range Nuclear Forces Treaty.”

McCain said the NDAA achieves a “delicate balance” that gives ULA time to transition to new technology.

“I believe avoiding the year-over-year re-litigation of this matter between our authorizing and appropriating committees is in our best interest, inasmuch as such back-and-forth only delay our shared to desire to eliminate Russian technology from our space launch supply chain and injects instability into the [Evolved Expendable Launch Vehicle] program – not conducive to its success in ensuring the reliable launch of our most sensitive national security satellites or the stability of the fragile industrial base that supports them,” he said.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.