Lawyers for Venezuelan migrants accused of being members of a violent street gang asked the Supreme Court on Tuesday to continue a temporary block on President Trump’s use of a wartime powers law to send hundreds of people to a prison in El Salvador.

The Trump administration has asked the justices to intervene and lift a block on the deportations imposed by a lower court. But a brief filed on behalf of the immigrants by the American Civil Liberties Union and Democracy Forward said that block is now “the only thing” preventing the Trump administration from sending immigrants “to a prison in El Salvador, perhaps never to be seen again, without any kind of procedural protection, much less judicial review.”

The government has already sent more than 130 Venezuelan men from the United States to El Salvador, according to the court filing, where the migrants “have been confined, incommunicado, in one of most brutal prisons in the world, where torture and other human rights abuses are rampant.”

The legal battle over the deportations of the Venezuelan migrants is one of the first major tests of Mr. Trump’s flurry of executive orders to reach the high court. It is perhaps the most high-profile of the eight emergency applications filed by the administration, focusing squarely on a collision between the judicial and executive branches.

There are typically no hearings or oral arguments for cases on the Supreme Court’s emergency docket, and there is no public schedule for a decision.

The 514-page filing, which included documents from the lower court and declarations from human rights experts, marks the latest turn in the legal fight over Mr. Trump’s efforts to remove immigrants accused of being members of Tren de Aragua, a street gang with roots in Venezuela’s northern Aragua state.