WASHINGTON  — The Supreme Court this week put an important check on President Trump’s power to arrest and quickly deport people who are alleged to be members of a foreign crime gang.

Those who face deportation “are entitled to notice and opportunity to challenge their removal” before a federal judge, the court said. They must be given “a reasonable time … that will allow them” to make their case on why they should be spared from deportation, the justices said.

“That means that the government cannot usher any detainees onto planes in a shroud of secrecy,” Justice Sonia Sotomayor wrote Monday.

She was referring to March 15, when three planeloads of detained men were flown from Texas to a maximum security prison in El Salvador.

Many of their family members said the men had no criminal records, and they had no warning they were being sent away.

The court this week did not decide on President Trump’s broad claims of a wartime power to deport “alien enemies.” It also left unresolved most questions about what happens next, including the possibility that the administration will not comply with a judge’s order.

But the justices agreed that all those facing deportation have a right to a hearing. It’s a decision likely to slow the pace of removals, but not to stop them.

It was just a month ago when the president, with no public notice, had signed a proclamation that Tren de Aragua, a Venezuelan crime gang, is a “foreign terrorist organization” that has invaded the United States.

Its members “shall be immediately apprehended and detained until removed from the United States,” he said.

The first two planes carried Venezuelans who were alleged to be members of the crime gang. The third plane included Salvadorans who were alleged to be members of MS-13, another crime gang. They included Kilmar Abrego Garcia, a Maryland man who denied he had been a gang member.

Six years ago, an immigration judge said he could not be sent to El Salvador because he could face persecution from gangs there.

The speedy mass deportation came to light that Saturday afternoon because ACLU attorney Lee Gelernt filed a lawsuit in Washington on behalf of five imprisoned men who said they were wrongly labeled as gang members.

His suit also questioned Trump’s assertion that the Alien Enemies Act of 1798 gave him war powers to arrest and deport “hostile” aliens.

A few days later, Abrego Garcia’s wife sued, seeking the return of her wrongly deported husband.

In response, Trump administration lawyers said the judges had no authority to second guess or question the president’s power to protect the nation from dangerous foreign gang members.

After losing in the lower courts, the administration’s lawyers filed fast-track appeals with Chief Justice John G. Roberts and the Supreme Court.

And this week, the court handed down a pair of unsigned orders that had a common theme shared by all nine justices: that the Constitution gives all persons, including noncitizens, a right to due process of law.

That means they cannot be arrested and deported by the government without an opportunity to appeal to a judge.

On Thursday, the court agreed with a judge from Maryland whose “order properly requires the Government to ‘facilitate’ Abrego Garcia’s release from custody in El Salvador and to ensure that his case is handled as it would have been had he not been improperly sent to El Salvador.”

That would allow him a hearing before a judge to argue why he should not be deported.

In recent weeks, Roberts has signaled he wants to avoid broad rulings in response to fast-track appeals. He is also fond of split-the-middle decisions that leave many to question who won and who lost.

But his focus on due process of law and the right to a habeas corpus hearing had several advantages. Judges, both liberal and conservative, agree on the importance of giving a fair hearing to someone who is the fighting the government.

Twenty years ago, the court agreed that the “war on terror” prisoners held at Guantanamo had a habeas corpus right to challenge their detention.

Justice Brett M. Kavanaugh, a former Bush White House attorney, wrote Monday the Guantanamo precedent calls for invoking the right to habeas corpus for the detained Venezuelans.

Such a ruling puts down a marker that can be a check on the Trump administration’s claim that the president alone had the power to decide who is arrested and deported.

It also will slow the pace of deportations. Hundreds of prisoners were deported on March 15 only because none of them were given a legal right to challenge their removal.

Gelernt of the American Civil Liberties Union called Monday’s order “an important victory. The critical point of this ruling is the Supreme Court must be given due process to challenge their removal.”

But as he and others noted, the court decided relatively little this week and left many questions unanswered.

It is not clear how or whether Trump and his administration’s lawyers will comply.

The administration conceded Abrego Garcia was wrongly deported because of its “administrative error,” but it has insisted that it had no duty to seek his return.

In response to Thursday’s order, the Justice Department restated its view that no judges may interfere.

“As the Supreme Court correctly recognized, it is the exclusive prerogative of the President to conduct foreign affairs. By directly noting the deference owed to the Executive Branch, this ruling once again illustrates that activist judges do not have the jurisdiction to seize control of the President’s authority to conduct foreign policy,” the department said.

On Friday morning, the Justice Department said it could not meet the judge’s deadline to provide an immediate update on the whereabouts of Abrego Garcia.

Because of all the uncertainty, Georgetown law professor David Cole said it’s not clear whether this week’s orders will prove significant.

“I think it’s too early to tell,” he said because the court did not rule directly on the president’s power over deportations.

It’s also not clear whether judges can or will block many deportations.

Judges in Texas and New York “have now ruled for individuals subject to [Monday’s] order, so the issue will get back up to the Court” soon, he said.