The American Civil Liberties Union (ACLU) and other advocates on Monday resumed a legal challenge against the U.S. government’s pandemic-era border policy of expelling migrants with little to no due process, saying months-long negotiations with the Biden administration had collapsed.

The lawsuit’s reinstatement could complicate the Biden administration’s efforts to deter migration to the U.S. southern border at a time when migrant apprehensions there remain at levels not seen in two decades.

At the center of the revived federal court case is a public health authority known as Title 42 that the Trump administration invoked in March 2020 to expel border-crossers, including asylum-seekers and unaccompanied children. Officials have argued the policy is needed to contain the spread of COVID-19.

The Biden administration exempted unaccompanied minors from the expulsions and has been allowing most families with children to seek humanitarian refuge, as outlined in U.S. law. But it has continued to defend Title 42 and use it to expel some migrant families and the vast majority of adults.

In February, the ACLU-led coalition of groups agreed to pause their lawsuit against the expulsion of migrant families under Title 42, saying they wanted to negotiate a resolution with the Biden administration, which had pledged to end Trump-era asylum restrictions.

The Biden administration made some concessions as part of the negotiations. But on Monday, the ACLU and the Justice Department filed a joint motion before the federal district court in Washington, D.C., saying those talks had reached an “impasse” and that litigation should resume.

“The Biden administration cannot possibly claim that it didn’t have enough time to end Title 42,” Lee Gelernt, the lead ACLU attorney in the Title 42 case, told CBS News. “The policy was never justified and certainly is not now, given the availability of testing and vaccines.”

The ACLU and other organizations like the Texas Civil Rights Project and the Refugee and Immigrant Center for Education and Legal Services have argued that expulsions of migrants are not authorized by public health law, which they don’t believe overrides U.S. asylum statutes.

Representatives for the Department of Homeland Security (DHS), which is implementing Title 42, did not respond to requests to comment on Monday’s announcement. Marsha Espinosa, a DHS spokesperson, said over the weekend that U.S. border officials continue expelling some families under Title 42 and that Mexico is accepting them.

During the first five full months of the Biden administration, U.S. officials have carried out over 513,000 expulsions from the southern border using the Title 42 authority, according to government data.

The policy has allowed the Biden administration to control the flow of most adults and some families crossing the border. But apprehension levels, inflated by migrant adults trying to cross more than once, have remained high.

Since March, apprehensions of migrants along the border with Mexico have remained above 170,000 for four consecutive months. In June, the last month with available statistics, U.S. border agents stopped or expelled migrants 188,000 times.

While most single adult migrants were expelled under Title 42 in June, just 14% of the 56,000 parents and children traveling as families were pushed back under the pandemic-policy.

In addition to the ACLU court case, the Biden administration is simultaneously facing another Title 42 lawsuit from Texas and the conservative America First Legal group that seeks to force the government to expel unaccompanied children and ramp up expulsions of families. 

In a lawsuit last year, the ACLU successfully argued before a federal judge that expelling unaccompanied children under Title 42 was illegal. The judge issued an order in November blocking the Trump administration from continuing the practice.