The supreme court has given the Trump administration a green light to turn back asylum seekers at the US-Mexico border, in a decision that fundamentally reshapes the US asylum system.

The Trump administration has sought for years to block migrants from setting foot on US soil, where federal law guarantees them the right to claim asylum and protection from persecution. The ruling will allow that practice to resume, concluding a battle that has spanned three administrations.

The vote was 6-3, with justices Samuel Alito, John Roberts, Clarence Thomas, Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett concurring. Justices Elena Kagan, Ketanji Brown Jackson, and Sonia Sotomayor all dissented, with the latter penning a biting 35-page long dissent – notably almost twice as long as the Alito majority opinion.

In Alito’s opinion, he wrote: “In ordinary speech, no one would say that a person ‘arrives in’ a place ... before the person enters that place.”

Sotomayor pushed back strongly in her dissent, explaining the dire consequences of the decision, noting that the government may now circumvent a vast range of laws protecting asylum-seekers by simply blocking their entry at the border.

“They may do so even if the asylum seeker is at the threshold of a port of entry designated to receive all noncitizens who seek entrance into the country. Even if the port of entry has ample capacity to inspect that person, including an available asylum officer trained to process asylum applications. Even if the asylum seeker is certain to be persecuted, or killed, if she is turned away,” she wrote.

She continued: ‘“The Court’s illogical interpretation is driven almost entirely by a fixation on a single word: ‘in.’ Words, however, must be read in context and with attention to how they fit into the statute as a whole. The majority ignores the statutory context and history, not to mention the longstanding position of the Executive Branch, all of which show that any noncitizen arriving at our doorstep and seeking admission must be inspected and allowed to apply for asylum, regardless of whether her foot has crossed the threshold. Because the Court today blesses the Executive Branch’s decision to slam the door shut on all who are fleeing persecution, despite the detailed inspection and asylum system that Congress enacted and commands, I respectfully dissent.”

The case was originally filed in 2017, during the first Trump administration, by Al Otro Lado, a legal and humanitarian service provider based in California and Mexico, and a group of asylum seekers subjected to the turnback policy.

At the time, the administration had vastly expanded the practice of turning back migrants at the border, leaving them stranded at dangerous encampments or temporary housing. Joe Biden rescinded the policy in 2021, but after Donald Trump was re-elected to the presidency, his administration asked the supreme court justices to review lower court rulings banning the practice.

US immigration law entitles migrants arriving in the US to seek asylum; the supreme court case hinged on what, exactly, it means to “arrive in”. When the court considered the case in March, chief justice Roberts and justice Barrett appeared to agree with the Trump administration’s argument – that to “arrive” in the US is to fully set food on US soil. If a migrant is turned back before they are able to cross the border, they are not entitled to asylum, the administration held.

The supreme court decision came after lower courts repeatedly invalidated the practice of turning away asylum seekers at the border. Advocates and attorneys representing migrants have argued that the practice is illegal and contrary to the country’s long history of providing refuge to those fleeing persecution.

But the Trump administration has long seen asylum as a roadblock in its goal of shutting down the southern border. Last year, administration officials promoted a global campaign to roll back asylum protections, seeking to dismantle the post-second world war framework supporting refugees and asylum seekers. During a United Nations gathering in September, deputy secretary of state, Christopher Landau, characterized the asylum system as “a huge loophole in our migration laws”.

The US Department of Homeland Security (DHS) under Trump has sought to not only turn away people arriving at the border, but also urged immigration courts to summarily dismiss asylum claims. Increasingly, the DHS has been sending migrants fleeing persecution in their home countries to third countries where they have never been.

A shift toward limiting access to asylum at the southern border, however, began during the Obama administration, when officials sought to “meter” the flow of migrants into the US. Asylum claims at the border had increased alongside dwindling opportunities for other types of immigration, and lengthy backlogs for visas and green cards. In 2016 tens of thousands of people from Haiti began arriving at the southern border seeking safety; many had first sought to settle in Brazil after the catastrophic 2010 earthquake, but made their way north after Brazil, too, experienced a stark economic downtown.

That’s when immigration agents, in some cases, began standing at international bridges, seeking to prevent migrants from reaching ports of entry to the US. Many who were turned away ended up stranded at camps without adequate food or access to medical care.

The Trump administration formalized the practice of turning back migrants at the border by stationing officers at the international border line to block asylum seekers from setting foot on US soil.

Though much of the supreme court oral arguments about the case centered on the question about what it means to “arrive” in the US and whether the administration is entitled to deny asylum by preventing arrival, the court’s liberal justices also grappled with what it would mean to essentially end the proactive of providing asylum at the US border.

Justice Sotomayor compared the practice of turning away asylum seekers to the tragedy of the St Louis, a passenger ship with Jewish refugees that was turned away from the US right before the second world war. About half the passengers who were returned to western European countries were trapped and killed when Germany invaded.