US President Donald Trump has issued a proclamation to deny asylum to migrants who enter the country illegally, tightening the border as caravans of Central Americans slowly approach the United States.
The plan was immediately challenged in court.
Trump invoked the same powers he used last year to impose a travel ban that was upheld by the Supreme Court. The new regulations are intended to circumvent laws stating that anyone is eligible for asylum no matter how he or she enters the country.
About 70,000 people per year who enter the country illegally claim asylum, officials said.
"We need people in our country, but they have to come in legally," Trump said Friday as he departed for Paris.
The American Civil Liberties Union and other legal groups swiftly sued in federal court in Northern California to block the regulations, arguing the measures were illegal.
"The president is simply trying to run roughshod over Congress's decision to provide asylum to those in danger regardless of the manner of one's entry," said ACLU lawyer Lee Gelernt.
The litigation also seeks to put the new rules on hold while the case progresses.
The regulations go into effect on Saturday. They would be in place for at least three months but could be extended, and don't affect people already in the country. The Justice Department said in a statement the regulations were lawful.
Trump's announcement was the latest push to enforce a hard-line stance on immigration through regulatory changes and presidential orders, bypassing Congress, which has not passed any immigration law reform.
But those efforts have been largely thwarted by legal challenges and, in the case of family separations this year, stymied by a global outcry that prompted Trump to retreat.
Officials said the asylum law changes are meant to funnel migrants through official border crossings for speedy rulings instead of having them try to circumvent such crossings on the nearly 3200kilometre border.
The US Border Patrol says it apprehended more than 50,000 people crossing illegally in October, setting a new high this year, though illegal crossings are well below historical highs from previous decades.
The US is also working with Mexico in an effort to send some migrants back across the border. Currently, laws allow only Mexican nationals to be swiftly returned and increasingly those claiming asylum are from Central America.
Trump pushed immigration issues hard in the days leading up to Tuesday's midterm elections, railing against the caravans that are still hundreds of miles from the border.