Jeff Bezos’ space company is escalating its fight with the US space agency.

Blue Origin, the space company owned by Amazon founder Jeff Bezos, filed a complaint Monday in federal court against NASA. The lawsuit escalates Blue Origin’s protest that NASA unjustly granted a lunar landing contract earlier this year to Elon Musk’s SpaceX.

“This bid protest challenges NASA’s unlawful and improper evaluation of proposals,” Blue Origin’s lawyers wrote in its court filing. The sealed complaint was filed in the US Court of Federal Claims.

NASA previously selected SpaceX as the sole provider for the Human Landing System for Artemis, the follow-up to the Apollo missions of the 1960s and early 1970s. The decision to go with SpaceX alone came as a shock to many who expected the space agency to select two companies to create the lander designs.

Blue Origins filed a formal protest in April. Last month, the Government Accountability Office denied the protest and upheld NASA’s selection of SpaceX for its human landing system.

Bezos unveiled Blue Origin’s Blue Moon lunar lander concept in 2019, but the development of the company’s spacecraft has lagged behind SpaceX in recent years. On July 20, Blue Origin completed its first crewed flight of the New Shepard rocket, with Bezos aboard. In April, SpaceX completed its third mission carrying astronauts to the International Space Station.

Blue Origin, NASA and SpaceX didn’t immediately respond to requests for comment.