The Biden administration and the American Civil Liberties Union said Monday that they have reached an “impasse” over the expulsions of migrant families at the southwest border and are returning to federal court to ask a judge to rule on the issue.

The move abruptly ends months of closed-door negotiations as the ACLU pressed for an end to the continued expulsion of migrant families under a public health order the Trump administration imposed during the pandemic.

The Biden administration had signaled that it wanted to lift the expulsions order and reopen the nation’s asylum system to migrants, but the spreading delta variant and fast-rising numbers of illegal border crossings prompted officials to back off plans to lift the order.

“The parties’ discussions attempting to resolve or narrow the dispute in this case have reached an impasse,” lawyers for the ACLU and the Biden administration said in a joint court filing Monday in the District of Columbia. “The parties therefore seek to resume litigation” on the issue, they said.

The development puts new pressure on the administration at a time when authorities are facing an overcrowding crisis inside Border Patrol stations and holding facilities in South Texas. Republicans have criticized the administration for easing Trump-era restrictions, while advocacy groups are demanding that President Biden reopen the border to asylum seekers.

Several immigrant advocacy organizations on Monday demanded that the administration terminate the expulsions immediately, saying they violated “long-standing immigration statutes requiring that asylum seekers receive a full and fair proceeding to determine their right to protection in the United States.”

“We gave the Biden administration more than enough time to fix any problems left behind by the Trump administration, but it has left us no choice but to return to court,” said ACLU lawyer Lee Gelernt. “Families’ lives are at stake.”

Trump officials began expelling hundreds of thousands of migrants to Mexico or their homelands in March 2020 under Title 42 of the public health code, arguing that the policy was needed to limit the spread of the coronavirus.

Biden had said he would reverse the Trump administration’s “inhumane” border policies, but his administration has struggled with the spike in crossings and the spread of the disease.

The CDC on Monday extended the order allowing authorities to quickly turn back border crossers, saying it would remain in place until it is “no longer necessary to protect the public health.” The Justice Department, which is defending the government in the ACLU’s lawsuit, said it had no comment Monday evening.

The Biden administration late Monday said in federal court records that enjoining the Title 42 order “will result in an immediate increased risk of harm from COVID-19” for DHS officials, immigrants and, potentially, the public.

Border Patrol officials are confronting a “historic” influx of migrants at the southwest border, a top official said in court records, with massive crowding in some Border Patrol sectors in Texas and more migrants and federal agents getting sick.

“Based on current trends, the Department expects that total encounters this fiscal year are likely to be the highest ever recorded,” David Shahoulian, assistant secretary for border and immigration policy at the Department of Homeland Security, said in the court filing. “The Department also expects that these numbers will climb even higher if the CDC Order is enjoined.”

The Biden administration has declined to call the situation at the border a crisis, but Shahoulian said in the court filing that the crowding in border detention is “extremely worrisome.”

Officials have made more than 1 million apprehensions at the southwest border this fiscal year as of June, and 210,000 more individuals probably crossed in July, he said, calling the preliminary tally “the highest monthly encounter number since Fiscal Year 2000.”

“July also likely included a record number of unaccompanied child encounters, exceeding 19,000, and the second-highest number of family unit encounters, at around 80,000,” which is close to the peak in May 2019.

“These capacity challenges are particularly acute with respect to families,” he said in the court filing. “DHS continues to have severely limited capacity to hold and process families, and the current migrant surge and ongoing pandemic have only compounded these issues.”

The lawsuit is before U.S. District Judge Emmet G. Sullivan, who blocked the Trump administration from expelling unaccompanied migrant children and teens in November. An appeals court panel of Trump-appointed judges lifted that ruling in January, but the Biden administration declined to resume expelling children traveling without their parents.

Sullivan on Monday ordered the ACLU and the government to file a report by Wednesday indicating whether they could resolve the dispute another way, such as via mediation.

Biden officials have warned migrants that many of them are still subject to the expulsion order, and flatly told them “do not come” to the United States. But officials also have exempted a rising number of migrants from the order, which critics say has encouraged more to come.

Two career Border Patrol agents in South Texas said they have never seen the sector so overwhelmed.

“It’s never been anywhere near this bad before,” said one agent who spoke on the condition of anonymity because the agent was not authorized to speak to reporters.

Brian Hastings, the sector’s Border Patrol chief, said in a court filing Friday that the “significant increase in apprehensions” has “strained the capacity” to hold migrants.

So many migrants have arrived this fiscal year that officials have had to transport them to other sectors, or detain them in an open-air enclosure under a highway bridge next to the banks of the Rio Grande. Drone footage of the site captured by Fox News shows families packed into a dusty holding area, where Customs and Border Protection has set up portable latrines and crates of water, snacks and diapers.

Hastings said the agency was holding more than 8,300 migrants in Rio Grande Valley border stations and tent facilities, up from fewer than 5,000 in early March, records show.

Hastings told the court that CBP has released more than 100,000 migrants in the Rio Grande Valley since October, of whom 9,000 were released last week. Most of the migrant families are processed into the United States and released from custody with a court hearing that affords them a chance to seek asylum.

His declaration was included in a suit by the Justice Department seeking to block an attempt by Texas Gov. Greg Abbott (R) to bar bus companies and other transportation firms from carrying migrants.