santa fe, new mexico - The U.S. government said Wednesday it is appealing a court ruling that would otherwise lift asylum restrictions that have become the cornerstone of border enforcement in recent years.

The disputed enforcement rule first took effect in March 2020, denying migrants' rights to seek asylum under U.S. and international law on grounds of preventing the spread of COVID-19.

The Homeland Security Department said it would file an appeal with the U.S. Court of Appeals for the District of Columbia, challenging a November ruling by U.S. District Judge Emmet Sullivan that ordered President Joe Biden's administration to lift the asylum restrictions.

The restrictions were put in place under former President Donald Trump at the outset of the COVID-19 pandemic. The practice was authorized under Title 42 of a broader 1944 law covering public health and has been used to expel migrants more than 2.4 million times. Many of those are repeated attempts to enter the U.S.

The appeal could scuttle a December 21 deadline set by Sullivan for his order to go into effect.

Sullivan has called the expulsion of migrants under the rule 'arbitrary and capricious.'

Immigrant rights' groups have argued that the use of Title 42 unjustly harms people fleeing persecution and that the pandemic was a pretext used by the Trump administration to curb immigration.

'The Biden administration's decision to appeal is unsurprising given its vigorous defense of the policy for the past two years,' said Lee Gelernt, an attorney for the ACLU and lead counsel on its Title 42 litigation, in an email.

A coalition of conservative-leaning states wants to keep the policy in place.

The ban has been unevenly enforced by nationality, falling largely on migrants from Guatemala, Honduras, El Salvador - as well as Mexicans - because Mexico allows them to be returned from the United States. Last month, Mexico began accepting Venezuelans who are expelled from the United States under Title 42, causing a sharp drop in Venezuelans seeking asylum at the U.S. border.

The asylum rule has been used by the Biden administration to expel migrant families and single adults, though not children traveling alone.