Justice Clarence Thomas wrote separately to say he would have granted the Trump administration’s request to block the lower court injunctions in their entirety while legal proceedings unfold. “Today’s compromise will burden executive officials with the task of deciding—on peril of contempt— whether individuals from the six affected nations who wish to enter the United States have a sufficient connection to a person or entity in this country,” he wrote. Samuel Alito and Neil Gorsuch joined his opinion.

In addition to the underlying issues at stake, the Court also asked both sides to file briefs on whether the second executive order expired on June 14. When Trump signed the order on March 16, it included a provision that Section 2(c)’s visa suspensions would only last for 90 days “from the effective date” of the order. Once Section 2(c) expires, legal challenges to it become moot.

The lower courts did not suspend that provision or even acknowledge it, meaning the 90-day clock theoretically kept ticking. Trump signed a memo on June 14 that claimed to amend the provision until legal proceedings conclude. “The Government takes the view that, if any mootness problem existed previously, the President’s memorandum has cured it,” the Court noted. But the justices nonetheless ordered both sides to weigh in on the question.

If the Court rules on the merits, the case is likely to result in a major precedent on the scope of the presidency’s national-security powers. It will also be Trump’s first showdown with the Supreme Court after months of battles in the federal appellate courts over his first and second executive orders on the travel ban. Presidents of both parties often find themselves stymied by the Court at some point during their administrations. But Trump will face a high-profile judicial test of one of his core policies far earlier than most of his predecessors.

In a statement shortly after the announcement, the president said he was “gratified” by the Court’s move. “Today’s unanimous Supreme Court decision is a clear victory for our national security,” Trump said. “It allows the travel suspension for the six terror-prone countries and the refugee suspension to become largely effective.”

The Department of Homeland Security said it would begin enforcing the ban after reviewing the ruling with the Justice and State departments. “The implementation of the executive order will be done professionally, with clear and sufficient public notice, particularly to potentially affected travelers, and in coordination with partners in the travel industry,” the department said in a statement.

The president signed the first iteration of his travel ban in January with little warning, leading to chaos and protests at major U.S. airports. Multiple federal courts soon blocked the government from enforcing the order pending judicial review. After a three-judge panel in the Ninth Circuit Court of Appeals approved a nationwide injunction against the ban in February, the administration said it would rewrite the order.