Boston, Massachusetts - President Donald Trump's administration was on Monday blocked by a federal judge from enforcing a policy that could see thousands of refugees arrested and detained.

US District Judge Richard Stearns in Boston ruled that new Trump administration rules are an unlawful departure from US migration policy that has existed for decades.

The policy, which Stearns blocked on legal grounds, could see thousands of refugees arrested and detained if they fail to obtain a green card within one year of arriving in the US.

Stearns issued the ruling in response to a lawsuit brought by six refugees and two advocacy groups, which argued that the Department of Homeland Security policy was unlawful.

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The plaintiffs said that if the policy were enforced, 100,000 legal refugees could face unlawful deportation and punishment despite waiting for their applications to be processed by US Citizenship and Immigration Services.

Stearns' decision "affirms that the government cannot manipulate the law to justify the mass arrest and detention of people," said Steven Bressler, a lawyer representing Democracy Forward.

"This ruling protects refugees from the Trump-Vance admin’s attempted cruel, unlawful treatment while our case proceeds," Democracy Forward wrote in a statement on X.

The policy in question is part of the DHS' "Operation PARRIS" strategy, which it introduced in January as an excuse to reexamine immigration cases and ramp up its mass deportation campaign.

Originally, the policy was designed to reexamine the cases of 5,600 refugees currently residing in Minnesota. It has since been expanded.

"This operation in Minnesota demonstrates that the Trump administration will not stand idly by as the US immigration system is weaponized by those seeking to defraud the American people," DHS said at the time.