Jeff Bezos' Blue Origin sued the U.S government over NASA's decision to award a $2.9 billion lunar lander contract to Elon Musk's SpaceX.

Blue Origin said its lawsuit filed in the U.S. Court of Federal Claims on Friday is  "an attempt to remedy the flaws in the acquisition process found in NASA's Human Landing System." It added it believes "the issues identified in this procurement and its outcomes must be addressed to restore fairness, create competition, and ensure a safe return to the Moon for America."

Last month, the Government Accountability Office (GAO) sided with the National Aeronautics and Space Administration over its decision to pick a single lunar lander provider, rejecting Blue Origin's protest.

Blue Origin's lawsuit remains under seal. NASA must file a response to the challenge by Oct. 12.

"NASA officials are currently reviewing details of the case," the agency said in a statement. "With our partners, we will go to the Moon and stay to enable science investigations, develop new technology, and create high paying jobs for the greater good and in preparation to send astronauts to Mars." The agency added, "as soon as possible, the agency will provide an update on the way forward for returning to the Moon as quickly and as safely as possible under Artemis."  

Blue Origin and defence contractor Dynetics have argued that NASA was required to make multiple awards. The GAO said it  "denied the protest arguments that NASA acted improperly in making a single award to SpaceX."  

Blue Origin, the rocket company founded by Amazon.com Inc's founder, billionaire Bezos, said earlier it remained convinced there were "fundamental issues" with NASA's decision and that GAO was not able to address them  "due to their limited jurisdiction."  Blue Origin said it will continue to advocate for two immediate providers as it believes that to be the right solution.

SpaceX, which is headed by Tesla Inc's CEO, Musk, did not immediately comment on Monday.

NASA had sought proposals for a spacecraft that would carry astronauts to the lunar surface under its Artemis program to return humans to the moon for the first time since 1972.

In April, NASA awarded SpaceX a contract to build such a spacecraft as early as 2024.

Blue Origin had contended NASA gave SpaceX an unfair advantage by letting it revise its pricing.

Bezos has offered to cover up to $2 billion in NASA costs if the U.S. space agency awarded Blue Origin a lunar landing contract.