Sierra Nevada is protesting NASA's decision to replace the shuttle with capsules developed by Boeing and SpaceX.
The company's legal challenge is unusual.
NASA has said little about why it chose Boeing and SpaceX to fly astronauts to the International Space Station and not Sierra Nevada.
Now Sierra Nevada has filed a protest with the Government Accountability Office.
Dan Gordon is an expert in procurement law at George Washington University.
He says most federal contracts go unchallenged.
"It's very rare that the GAO issues a decision saying that the contracting agency violated procurement law. That happens a few dozen times a year out of the 2,000 or so cases the GAO gets each year."
Sierra Nevada says its proposal meets NASA's criteria and provides a better value.
Gordon says it's possible Sierra Nevada will end up flying astronauts to the ISS if the company can get NASA to voluntarily review its decision.
"A fifth of the time, one out of five cases, the protester ended up with a contract. For an important contract that's a very big deal. For Sierra Nevada those odds are not bad at all."
Gordon says NASA must decide whether to review its decision or fight Sierra Nevada's legal action.
NASA awarded contracts to Boeing and SpaceX this month. The announcement makes way for American-based human spaceflight to resume by 2017.
