SpaceX founder Elon Musk took aim at NASA's acting administrator Sean Duffy on X, after Duffy announced that NASA will open SpaceX's moon lander contract up to competitors.

After NASA's head indicated SpaceX could lose its moon lander contract, Elon Musk went on the attack on X against Sean Duffy.

Acting NASA chief Sean Duffy and billionaire Elon Musk on Tuesday traded barbs online over who should lead the space agency, a day after Duffy invited companies to compete with Musk's SpaceX for a moon landing mission.

Earlier this week, Transportation Secretary and NASA acting administrator Sean Duffy suggested that SpaceX may not be the first American company to return the space agency's astronauts to the moon. NASA's Artemis III mission,

NASA's acting administrator accused SpaceX on Monday of falling "behind" and said he plans to reopen contracts to get U.S. astronauts "back to the moon in 2028."

NASA wants companies to compete with SpaceX over a contract it holds to put astronauts on the moon, a fresh sign of blowback over delays with Elon Musk’s Starship spacecraft.

Interim NASA Administrator Sean Duffy said Monday that NASA was reopening the contract for the Artemis III moon lander after delays with development of SpaceX's Starship.

NASA says it's considering bids from other private space companies over concerns that Elon Musk's SpaceX is behind schedule. Musk fired back on X, writing, "SpaceX is moving like lightning compared to the rest of the space industry.