Drawing on national security powers, the Departments of Homeland Security and Justice issued a fast-track rule barring immigrants from seeking asylum if they first enter the USA illegally.
The American Civil Liberties Union said that right of asylum must be granted to anyone entering the country, regardless of where they were.
The new rules are subject to a presidential proclamation expected Friday in which Trump will invoke the same justification he did for the travel ban. "It is illegal to circumvent that by agency or presidential decree", Omar Jadwat, director of the ACLU's Immigrants' Rights Project, responded in in a statement.
Administration officials have said existing USA asylum rules encourage illegal immigration and bog down legitimate claims.
This is expected to put a dent in those streaming into an already overburdened system, officials said, noting that there is a backlog of more than 700,000 cases in the immigration courts.
Later, at a campaign rally in Missouri, Trump offered additional remarks on the topic, saying, "Under this plan, the illegal aliens will no longer get a free pass into the country by lodging meritless claims in seeking asylum".
Trump made immigration a key issue in Tuesday's election, stoking fear among his supporters about a migrant caravan that's still hundreds of miles away in Mexico.
"What we are attempting to do is trying to funnel. asylum claims through the ports of entry where we are better resourced, have better capabilities and better manpower and staffing to actually handle those claims in an expeditious and efficient manner", a senior administration official told reporters in a news briefing Thursday, on condition of anonymity.
Last week, he said he would be taking steps to limit asylum claims.
The interim final rule posted Thursday from the Justice Department and Department of Homeland Security would bar immigrants who cross the "southern border unlawfully" from "eligibility for asylum".
In 2017, the US fielded more than 330,000 asylum claims, almost double the number two years earlier and surpassing Germany as highest in the world.