Blue Origin, the space company owned by Jeff Bezos, is suing the US government over its decision to award a massive Moon exploration contract to its competitor SpaceX, it said in a statement Monday.

The company has filed a suit with the US Court of Federal Claims "in an attempt to remedy the flaws" in how the contract was awarded, according to the statement. 

The human landing system (HLS) contract, worth $2.9 billion, was given to SpaceX, owned by Bezos's billionaire rival Elon Musk, in April. 

It was protested by the other bidders, who argued NASA was required to make multiple awards and that the evaluation process was unfair.

"We firmly believe that 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," Blue Origin said.

Since losing the contract, Blue Origin has strongly lobbied to have the decision reversed. It filed a protest with the Government Accountability Office, but in July the watchdog upheld NASA's decision.

NASA said in a statement Monday that it was notified of Blue Origin's lawsuit and it is reviewing the case. 

"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 statement said.

Under the Artemis program, NASA is planning to return humans to the Moon in the middle of this decade and build a lunar orbital station, before a crewed mission is sent to Mars in the 2030s.

Musk's company, founded in 2002, is currently NASA's leading private sector partner.