Judge Emmet Sullivan says the rule, which has been used to expel hundreds of thousands of people since being invoked in the early days of the Covid-19 pandemic, was an "arbitrary and capricious" policy that violated government procedures.
A US federal judge has ruled that the government could not use public health rules to block the entry of asylum-seeking migrants.
Judge Emmet Sullivan said Tuesday that Title 42, which has been used to expel hundreds of thousands of people since being invoked in the early days of the Covid-19 pandemic, was an "arbitrary and capricious" policy that violated government procedures.
The ruling leaves the government with few tools to block the entry of migrants at the southern border with Mexico, most of whom ask for asylum.
More than 200,000 have been interdicted each month this year, with many being dealt with under Title 42 -- a 19th-century provision designed to prevent the introduction of contagious diseases.
Sullivan also ordered that the government could not seek a stay on his ruling to block its implementation, meaning authorities will have to appeal it to a higher court if they want it to remain in place.
Migrants have been expelled from the United States more than 2.4 million times since the rule took effect in March 2020, denying migrants rights to seek asylum under US and international law on grounds of preventing the spread of Covid-19.
The ruling came after a lawsuit brought in January by the American Civil Liberties Union, which accused the Department of Homeland Security and Border Patrol of "summary expulsion" of vulnerable families seeking asylum who showed no signs of Covid infection.
"This is a huge victory and one that literally has life-and-death stakes," said ACLU attorney Lee Gelernt, who led the lawsuit.
"We have said all along that using Title 42 against asylum seekers was inhumane and driven purely by politics. Hopefully, this ruling will end this horrific policy once and for all," he said in a statement.
The ruling came six months after a Louisiana judge ruled in a separate suit that the administration of President Joe Biden, which inherited the Title 42 policy from Donald Trump, could not drop it.
The judge, in that case, said ending the use of the Title 42 rule would violate official government procedures.
While the Biden administration had wanted to end the use of Title 42, it has at the same time continued to rely heavily on the policy as it battles surging migrant numbers at the southern border -- a toxic political issue that Republicans pushed heavily in the run-up to last week's midterm elections.
But critics branded Title 42 "inhumane," and said it was an ad-hoc immigration plan dressed up as a health policy, but fit for neither purpose.
The measure allows for the immediate removal of any foreigner or non-resident trying to enter the country without a visa.
There is no legal process, or any formal deportation to the country of origin, and a border agent can apply for a Title 42 expulsion without the lengthy interview process usually required.
Aaron Reichlin-Melnick, director of policy for the American Immigration Council said Title 42 had been "a failed border management policy that caused chaos along the border, immeasurable harm to innocent people seeking our protection, and diminished our standing on the world stage."