The U.S. Supreme Court has allowed full enforcement of President Trump's latest asylum crackdown.
Trump had been seeking a new rule which forbids almost all migrants from seeking asylum at the southern border.
Wednesday's (September 11) ruling will see it enforced- after months of dispute which began in July when the rule was unveiled.
It means migrants who pass through other countries to get to the U.S. - must first apply for asylum in a third country.
Only if their application is denied - can they then seek asylum in the US.
In practice, the rule will block migrants from countries like El Salvador, Honduras, or Guatemala from crossing over the border with Mexico.
Many are fleeing poverty and crime.
The court allowed the rule to go into effect on Wednesday as litigation challenging its legality continues.
It's a major victory for Trump, whose hard line on immigration has been a hallmark of both election bids.
He tweeted - BIG United States Supreme Court WIN for the Border on Asylum.
Opponents of the policy say it violates U.S. immigration law, and accuse the administration of failing to follow correct legal processes.
Two liberal judges dissented - Justice Sonia Sotomayor said the rule:
"topples decades of settled asylum practices and affects some of the most vulnerable people in the Western Hemisphere - without affording the public a chance to weigh in."