– A fight over the use of Russian rocket engines to launch U.S. military satellites has ignited a lobbying battle in Congress among a handful of commercial space industry giants, sparking concerns in Houston about the potential fallout for NASA’s Johnson Space Center.

The controversy, involving hundreds of millions of dollars in government contracts, rose Thursday as lawmakers scrambled to put the finishing touches on a sweeping $602 billion defense bill.

President Obama, citing national security concerns over restricting the Russian engines, has threatened to veto the entire bill, which includes other controversial provisions.

Fueling a debate over American dependence on the popular RD-180 engine are rising geopolitical tensions over the Ukraine. At the same time, a group of Houston business leaders has joined some aerospace industry officials in warning about the potential costs of banning the Russian-made rockets too quickly.

Among them is Bob Mitchell, president of the Bay Area Houston Economic Partnership.

“We urge you to strongly consider the consequences of blocking access to the RD-180 for political reasons before a reliable and affordable domestic alternative is available years from now,” Mitchell wrote to Texas U.S. Sens. John Cornyn and Ted Cruz. “Prematurely ending the use of the RD-180 would also have far-reaching negative impact to the space industry, which employs 14,000 highly technical skilled people in the Houston area.”

Although the proposed restrictions apply only to the military, some officials worry that they could increase costs for NASA’s commercial crew and cargo shipments for the International Space Station, which rely on Atlas V rockets powered by RD-180 engines.

“With the military out of the picture, a sharp drop in Atlas V launches overall may make overhead costs for NASA use prohibitive,” Mitchell said. “This could undermine NASA planning for the next decade.”

Opponents of the RD-180, led by Arizona Sen. John McCain, chairman of the Senate Armed Services Committee, say there would be no impact on NASA, thanks to new rockets being developed by SpaceX and United Launch Alliance (ULA), a joint venture of Boeing Co. and Lockheed Martin Corp. that has served as the Pentagon’s main launch provider.

However, questions remain about how quickly those new rocket engines can be made available, and the increased costs of currently available U.S. heavy-launch alternatives to the Atlas V, which have been estimated in the billions.

A bill passed by the House last month grants Denver-based ULA up to 18 Russian-made engines for national security launches over the next five years. Senate language pushed by McCain would cut that number to nine.

Pentagon officials have testified that current alternative launch vehicles, including ULA’s Delta IV and SpaceX’s new Falcon 9, are too expensive or unworkable for the near term.

ULA argues that until a replacement is found, the Atlas V remains the most effective launch vehicle for NASA and the military.

Behind the scenes, California-based SpaceX has backed efforts to limit ULA’s continued reliance on the RD-180.

SpaceX and its backers also dismiss any impact on NASA, arguing that the civilian agency has fixed-price contracts for its launch hardware, meaning ULA, not taxpayers, would have to absorb any increased costs from dropping the RD-180.