A coalition of immigrant advocates, including the American Civil Liberties Union, sued the Trump administration in federal court in Washington on Monday, arguing that President Trump’s order shutting the United States’ southern border to asylum seekers was unlawful.

The lawsuit is the first challenge to President Trump’s broad efforts to close the border in an executive order issued on Jan. 20. Mr. Trump’s order argued that infrastructure there was not equipped to adequately screen people’s backgrounds. He determined that there was an “invasion” that required him to block migrants from entering through the southern border until it was stopped.

“Under this proclamation, there’s no longer asylum, period,” said Lee Gelernt, a lawyer with the A.C.L.U. leading the challenge. “Countless people, including families with small children, will be returned to danger, maybe to their death. Plain and simple, this is a power grab at the expense of Congress.”

The administration did not respond immediately to a request for comment.

During the first Trump administration, U.S. officials tried several times to restrict the asylum system. Some of those efforts were struck down by the courts.

The challenge filed on Monday is the latest attempt to overturn one of Mr. Trump’s immigration policies in court. A federal judge in Seattle has already temporarily blocked a different order by Mr. Trump that sought to restrict birthright citizenship, which is guaranteed in the Constitution.

The lawsuit filed on Monday argues that Mr. Trump’s order has led to the quick deportation of migrants, denying them any meaningful access to asylum in violation of U.S. law.

“Asylum seekers are also being systematically expelled from the United States without being provided credible fear interviews — the absolute minimum that Congress required to ensure that people subjected to expedited removal would not be returned to persecution or torture,” the lawsuit asserts, referring to asylum screenings at the border.

Lawsuits against Mr. Trump’s first administration blocked several of his more contentious policies, including an effort to limit asylum protections in 2018.

“Whatever the scope of the president’s authority, he may not rewrite the immigration laws to impose a condition that Congress has expressly forbidden,” a federal judge in San Francisco, Jon S. Tigar, wrote in his order blocking that policy in November 2018.

Former President Joseph R. Biden Jr. also limited asylum for migrants who crossed the border illegally last year. His order, however, allowed for migrants to have full access to the system if they entered through a port of entry or other pathways Mr. Trump has either closed or frozen in the weeks since his inauguration last month.