The ruling means that US Customs and Border Protection can immediately begin denying migrants asylum at the southern border if they haven't first applied for safe haven in a "third country" while the greater legal battle over the issue plays outin the lower courts. 

Dissenting from Wednesday's decision were Justices Ruth Bader Ginsburg and Sonia Sotomayor. 

San Francisco Federal Judge Jon Tigar issued a preliminary injunction in July blocking the policy after a coalition of migrant and civil rights groups represented by the American Civil Liberties Union challenged the rules in court, while the 9th US Circuit Court of Appeals narrowed Tigar's injunction - relegating it to within the 9th Circuit's jurisdiction. According to the Daily Wire's Kevin Daley, "That meant that the third-country transit bar could be applied to migrants intercepted in New Mexico or Texas, but not Arizona and California," adding that "the 9th Circuit also said Tigar could reimpose a nationwide injunction if he made additional factual findings supporting such a move. Tigar did so and restored a nationwide injunction against the contested rule Monday."