The US Supreme Court has given the go-ahead to Trump administration plans that severely limit the ability of migrants to claim asylum.
Under the rule, people arriving via a third country must claim asylum there first before arriving at the US border.
Legal challenges against it continue but the ruling means for now it can be enforced nationwide.
The plan will affect tens of thousands of Central American migrants who travel north, often on foot, through Mexico.
The Trump administration unveiled the new asylum policy in July but it was almost immediately blocked from taking effect by a lower court ruling by a judge in San Francisco.
Curbing migration levels has been a key goal of Donald Trump’s presidency and forms a major part of his bid for re-election in 2020.