Hundreds of millions in U.S. taxpayer dollars could be spent on Russian rocket engines if a tiny section slipped into the annual defense spending bill is ultimately passed.

Senator John McCain, the chairman of the Senate Armed Services Committee, is furious, calling it a benefit to “Vladimir Putin’s cronies”—and accusing a fellow Republican of trying to keep the cash flowing to Moscow. But the reality is there may not be an alternate to the Russian engines—at least not in the short term.

McCain has previously led an effort to ban the purchase of the Russian-made RD-180 engine, which is used to power Pentagon and U.S. intelligence community space launches, by 2019. He views the section in the appropriations bill as a threat to his prohibition.

“Why in the world would anyone think we would want to continue dependency on Russian rocket engines, which traces up to the corrupt mafia that is around Vladimir Putin?” McCain told The Daily Beast. “The American people should ask a question of these appropriators: Why are you taking care of Vladimir Putin’s cronies?”

The apparent bid to weaken McCain’s prohibition is being led by the powerful chairman of the Senate Banking Committee, Alabama Senator Richard Shelby, a fellow Republican.

“I know why,” McCain said. But he didn’t want to expound on whatever knowledge he might have. Nor did Shelby want to discuss the matter. Asked about the Russian rocket engines, he wouldn’t answer a question about why he supported their purchase—pointing only to the transcripts of his prior questioning of Pentagon officials.

RD-180s are used in this country by United Launch Alliance, the consortium responsible for the vast majority of America’s national security space launches. It’s a major employer in Alabama, Shelby’s state. In 2013-14, Boeing and Lockheed Martin, which jointly run United Launch Alliance, contributed nearly $160,000 to Shelby’s campaign committee and leadership PAC.

ULA operates a 1.6 million-square-foot rocket factory in Alabama. Shelby has been a major supporter of United Launch Alliance, which has hired approximately 1,000 of his constituents.

The use of a Russian-made engine for U.S. government space flights was the result of cooperation between the U.S. and Russian defense industries after the Cold War. The Atlas V supports the majority of U.S. national security space launches. It’s the workhorse of the American fleet. And as The Daily Beast previously noted, it’s built around the RD-180.

But political circumstances have changed dramatically in recent years, in particular since the Russian 2014 invasion of Crimea and its subsequent military actions in eastern Ukraine.

The question remains, however: If not the Russian-made engine, what will power the United States’ rockets into space? McCain’s law sets a 2019 timeline for the creation of a new American-made rocket engine, which the Air Force has pushed back against, arguing that the deadline may be unrealistic.

“All of the technical experts with whom I have consulted have told me this is not a one- or two- or three-year deal,” the secretary of the Air Force, Deborah Lee James, told a congressional panel in February. “You’re looking at six years, maybe seven years to develop an engine, and another year or two beyond that to integrate. This truly is rocket science. These are hard technical problems, and so to have that 2019 date there is pretty aggressive, and I’m not sure we can make it.”

Concerns over the engine have become something of a proxy fight between two competitors in the rocket manufacturing market, traditional monopoly-holder United Launch Alliance and new entrant SpaceX, the rocket maker run by Tesla Motors CEO Elon Musk.

United Launch Alliance, which uses the RD-180 engine, argues that the Russian engine prohibition sets it back in competition against SpaceX, which in turn says it has the capability to meet the nation’s launch requirements now.

SpaceX’s Falcon vehicles use U.S.-built engines, as does United Launch Alliance’s Delta vehicles. But the Air Force secretary has questioned whether the Delta system is too costly to be competitive—culminating in her concern that the Russian-rocket prohibition essentially replaces the United Launch Alliance monopoly with a SpaceX monopoly.

Previously United Launch Alliance had a monopoly over U.S. government payloads launched into space. But SpaceX has become certified to compete and win contracts.

Since McCain started his effort to gradually discontinue the use of Russian-made engines by 2019, Shelby has been at the forefront of softening the prohibition.

A Shelby spokesperson said the senator “would like to see a transition away from the RD-180 engine” at some point and has supported hundreds of millions in appropriations to develop a new alternative engine. But that will not be available for at least several years.

United Launch Alliance has also urged for softening the law. Citing comments by James, ULA spokeswoman Jessica Rye said “a clarification in the [McCain’s Defense Department policy legislation] is needed to ensure the nation responsibly transitions from the RD-180 to a domestic alternative in a way that does not impact the launch of our national security payloads.”

The current debate is over how many additional Russian-made RD-180 engines may be purchased for use by the U.S. government.

United Launch Alliance has said it needs to use at least 14 engines. The House’s version of the annual defense policy bill allows it to use all 14, while the Senate version allows it to use no more than nine, according to Breaking Defense.

McCain has said the purchase of Russian-made rocket engines in the interim could funnel some “$300 million for Vladimir Putin and his cronies.”

Which brings us to the Senate’s defense appropriations bill. Deep in the legislation, in Section 8045, there’s a provision that was apparently written to undermine McCain’s efforts to fight Russian-made engines.

The appropriations language says competitions for the Air Force’s space launches in fiscal year 2016 must consider bids from at least two providers. In reality, there are only two possible competitors, SpaceX and United Launch Alliance, which means a failure to bid by the latter could gum up the Air Force’s program.

The language “empower[s] a private company to disrupt the Air Force’s launch program by holding a program hostage by not offering bids,” an industry insider said.

If United Launch Alliance does not get the legislative relief it wants—the ability to use and purchase more Russian-made engines—it could conceivably prevent SpaceX From being awarded the contract.

McCain certainly views the language as a threat to his effort to phase out the Russian-made engine. “It’s outrageous,” he said of the appropriations section.

The defense appropriations bill could be brought up again before the Senate as early as this week.