US President Joe Biden's administration has unveiled a plan that would make it harder for migrants to claim asylum once Covid border controls lift in May.
It would require adult asylum seekers to use an app to book a meeting with US officials or first claim asylum in another country before reaching the US.
Failure to comply would make migrants ineligible if they subsequently reach the border.
Pro-migrant groups likened the plan to Trump-era policies.
Tuesday's proposed measure is the toughest to curtail immigration yet introduced by Mr Biden, a Democrat who came into office promising a more humane approach to the border crisis than the administration of his predecessor.
The proposed rule would only apply to adults and families, but not to unaccompanied children.
Under the plan, migrants would have to use a phone app to make an appointment to speak with a US immigration official when they arrive at the border.
Those who failed to make the appointment would be presumed to have been found ineligible for asylum in the other countries they passed through.
The proposal - issued jointly by the US Department of Homeland Security and the Department of Justice - allows for those undocumented migrants to be swiftly deported.
If approved, it would be enacted on 11 May, when Title 42 - a Trump-era health emergency provision allowing migrants to be expelled back to Mexico - is due to expire.
The Biden policy would remain in place for two years with the option of extending it.
The American Civil Liberties Union (ACLU) said it would sue to block the rule from ever taking effect.
The organisation compared the plan to actions previously taken by former President Donald Trump that were ruled unconstitutional in the courts.
Oxfam America said: "This sweeping asylum ban will shut the door to countless refugees seeking safety and protection in the United States."
But an unnamed Biden administration official told AFP news agency: "This administration will not allow mass chaos and disorder at the border because of Congress's failure to act."
The public has 30 days to comment on the draft proposal.
About 200,000 undocumented migrants attempt to enter the US each month, recent government records show.
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