SpaceX has filed a protest challenging the nearly $150 million contract that NASA recently awarded to its chief rival, a joint venture between Lockheed Martin and Boeing, the latest salvo in an ongoing war between the companies over lucrative rocket launch contracts.

In a statement, SpaceX, the California company founded by Elon Musk, said it was the first time it had challenged a NASA contract.

“SpaceX offered a solution with extraordinarily high confidence of mission success at a price dramatically lower than the award amount,” the company said in a statement to The Washington Post. “So we believe the decision to pay vastly more to Boeing and Lockheed for the same mission was therefore not in the best interest of the agency or the American taxpayers.”

United Launch Alliance, or ULA, is the company Lockheed Martin and Boeing formed to compete for government launch contracts. It has long heralded the reliability of its Atlas V rocket and in a statement said: “This interplanetary mission has an extremely narrow launch window in order to reach all of the desired planetary bodies and accomplish the science objectives. If Lucy misses this launch window, the full mission cannot be accomplished for decades.”

NASA said that as a result of the protest it had issued a stop-work order, preventing ULA from preparing for the mission. It declined to comment further.

SpaceX and ULA have been battling for years. In 2014, SpaceX filed suit against the Air Force, asserting that the company should be able to compete for the national security launch contracts that for a decade were ULA’s main revenue source and for which ULA was the Pentagon’s only provider.

At the time, ULA fired back, saying that SpaceX couldn’t be trusted to launch such critical satellites and that it was trying to “cut corners” to win the lucrative contracts.

SpaceX responded by saying “ULA doesn’t believe in competition. Monopolists never do.”

SpaceX settled the lawsuit with the Air Force in 2015 and eventually won the certification that would allow it to compete against ULA. Since then, it has won several contract awards and completed one mission, the launch of a GPS satellite.

This week, the Pentagon’s inspector general’s office announced it was reviewing SpaceX’s certification. The office did not say what prompted the review but called the audit “self-initiated.”

The NASA contract was awarded to ULA last month to launch a spacecraft named Lucy to explore the Trojan asteroids around Jupiter on a journey that would take 12 years.

In a news release, NASA said the asteroids are “clusters of rocky bodies almost as old as the sun itself, and visiting these asteroids may help unlock the secrets of the early solar system.”

The mission, to be launched in October 2021, requires a precise launch window so that the spacecraft can “throw itself out into a celestial alignment that will not occur for decades.”

The SpaceX protest was filed Monday with the Government Accountability Office, which typically has 100 days to review challenges to contract awards.