The Biden administration has said it will indefinitely extend a Trump-era pandemic policy that allows the US to swiftly expel undocumented migrants.
The policy known as Title 42 is aimed at preventing the spread of Covid-19 in holding facilities, officials say. Children and some families are exempt.
At least 940,000 people have been expelled since it was issued last year.
The decision comes as migrants continue to stream to the US border, including about 210,000 in July alone.
In a statement, the US Centers for Disease Control and Prevention (CDC) said that the policy will remain in effect until the spread of Covid by non-citizens stops being a “serious danger” to public health.
The CDC said it will review the situation every 60 days.
The announcement drew outrage from immigration advocacy groups who accused the Biden team of backing the hardline anti-immigration policies of Donald Trump.
Officers from Customs and Border Protection encountered an average of 6,779 individuals each day in July, including 616 unaccompanied children, Monday’s court filing said.
It added that the “record numbers” of migrants had “strained” operations at the Department of Homeland Security (DHS), according to David Shahoulian, the assistant secretary for border and immigration policy.
“These encounter rates have … caused border facilities to be filled beyond their normal operating capacity, impacting the ability to employ social distancing,” the filing quoted Mr Shahoulian as saying.
Additionally, Mr Shahoulian said that the department is experiencing “significantly increased rates” of positive Covid tests. It added that the dangers have increased because of the spread of the highly transmissible Delta variant.
The American Civil Liberties Union and several other advocacy groups have said they will return to court over President Biden’s use of Title 42.
His administration has repeatedly defended the Trump-era policy in courts, where the civil rights groups have sued to have the US asylum system continue processing claims.
While the Biden government has made immigration reform an important goal, the president has repeatedly called on migrants to not attempt the dangerous journey to the US.
“I can say quite clearly: don’t come over,” he said in an ABC News interview in March. “We’re in the process of getting set up. Don’t leave your town or community.”