A federal appeals court is set to hold a hearing Tuesday, June 17, on whether President Donald Trump can continue to control California’s National Guard troops and deploy them to help with his administration’s immigration enforcement operations and the massive protests that have followed.

But ahead of that hearing, Trump issued a message.

Immigration and Customs Enforcement officials are “ordered,” the president said in a post on his Truth Social account Sunday evening, to carry out “the single largest mass deportation program in history.” And that means expanding immigration efforts targeting the country’s largest cities, including Los Angeles, Trump said.

At the heart of Tuesday’s hearing, though, is Trump’s use of California’s National Guard for his immigration plans.

Trump earlier this month federalized the state’s National Guard, moving more than 4,000 troops to Los Angeles to respond to large-scale demonstrations over immigration enforcement efforts.

The administration made those moves without the consent or request of Gov. Gavin Newsom; the Democratic governor later sued, requesting a temporary restraining order to halt the National Guard troops from being used to enforce immigration or civil laws in the state.

U.S District Judge Charles R. Breyer granted the restraining order, calling Trump’s actions “illegal” and ordering the National Guard back under the command of Newsom. His ruling said the court “must determine whether the president followed the congressionally mandated procedure for his actions. He did not.”

Trump’s legal team immediately appealed, and the 9th Circuit Court of Appeals temporarily blocked Breyer’s ruling only a few hours after it had been issued, setting a hearing to be held Tuesday. Trump, therefore, remains in control of the state’s National Guard for now.

That immediate stay indicates that the court is taking “very seriously” the matter before it, said Kyle Longley, an expert in military history who has studied large-scale demonstrations and unrest throughout U.S. history.

“Staying it so quickly is a definite sign that they’re questioning whether the president had the authority or reason to respond in the way that he did,” Longley, who teaches history at Chapman University, said.

Trump’s use of the National Guard certainly isn’t he first time a president has done so in U.S. history, Longley noted.

There were the times the National Guard was called in to assist amid desegregation efforts in the South. The Michigan National Guard was deployed in Detroit during a six-day uprising in 1967.

And closer to home, then-President George H.W. Bush invoked the Insurrection Act in 1992, deploying troops to Los Angeles during the unrest that came after four White officers charged with beating Black motorist Rodney King were acquitted. National Guard troops, about 8,000 of them, were also deployed throughout California by Newsom to assist police during the protests that followed the death of George Floyd in Minnesota.

But in many of these previous times National Guard troops were mobilized, the governor was on board, said Longley.

The last time a president called up National Guard troops without a governor’s support was in 1965 when then-President Lyndon Johnson sought to protect civil rights activists in Alabama, according to the Brennan Center for Justice, a nonpartisan law and policy group.

“That is completely absent now,” said Longley.

Newsom and Los Angeles Mayor Karen Bass “are definitely saying, ‘We don’t want you; we don’t need you. This is a political stunt,’” Longley said. “I’ll be watching to see what kind of historical precedent they (the appeals court) use, what kind of legal precedent.”

California Attorney General Rob Bonta said he was “confident” ahead of Tuesday’s hearing that judges will determine Trump could not appropriately use what’s called Title 10 of the federal code. That allows a president to federalize a state’s National Guard if the country is “invaded,” if there is “a rebellion or danger of a rebellion against the authority of the government” or if the president cannot otherwise “execute the laws” of the country.

“There’s absolutely no invasion or rebellion (or) inability of the federal government ot execute laws,” Bonta said in an interview Monday morning.

Trump, members of his Cabinet and his spokespeople have repeatedly defended his federalization of the National Guard amid his immigration enforcement operations.

Trump has alleged that without his calling up the National Guard, protesters would “rip Los Angeles apart.” White House spokesperson Anna Kelly previously told the Southern California News Group that Newsom “should thank (Trump) for restoring law and order.”

The appeals court hearing is scheduled for June 17 at noon before a three-judge panel of Mark Bennett, Eric Miller and Jennifer Sung. Bennett and Miller were both appointed by Trump; Sung was appointed by former President Joe Biden.

Tuesday’s hearing will be livestreamed. Check out the court’s website for more information.

Bonta said the state’s arguments “remain just as strong in front of the appellate court,” but acknowledged this might not be “the last stop” in the legal battle. It’s possible, with continued appeals, this legal fight between Newsom and Trump could not be settled until it reaches the U.S. Supreme Court.

Staff writer Jonathan Horwitz and The Associated Press contributed to this report.