SACRAMENTO — Leaders of California’s high-speed rail project told the Trump administration Monday its plans to withhold or claw back $3.5 billion in federal money for the project was “legally indefensible” and “disastrous policy.”

Terminating the money “would cause massive disruption, dislocation, and waste, damaging the region and endangering the future of high-speed rail in California and elsewhere in the nation,” Brian Kelly, the chief executive for the project, wrote in a letter to Jamie Rennert of the Federal Railroad Administration.

Kelly’s letter is in response to a February threat by the U.S. Department of Transportation to withhold a $929 million grant for the project and possibly take back $2.5 billion in federal money the state has already spent.

Congress and the Obama administration allocated the money almost a decade ago for California to build a high-speed rail line between Los Angeles and San Francisco. A segment of the train in the Central Valley is now under construction, and the $3.5 billion is a key piece of its budget.

The threat was an escalation in California’s ongoing feud with the Trump administration. It came after Gov. Gavin Newsom suggested changes to the project in his State of the State address. He said the project as currently planned would cost too much and take too long, and said he wanted to focus first on building a longer line in the Central Valley.

Newsom has since said he still intends to build the full line, but Trump used his comments to decry the project as a “failure.” Newsom said Trump’s call to take back the money was retaliation for the state’s lawsuit against the president’s declaration of a national emergency at the U.S.-Mexico border.

California must meet certain construction and environmental review deadlines by 2022 as part of its agreement with the federal government. Kelly said the state is meeting its obligations and that the vision of the project has not changed.

He said the threat to withhold the roughly $1 billion the state hasn’t yet received was not legally defensible, and that efforts to take back what’s already been spent “disastrous policy.”