The new proposal, which was telegraphed in a January news conference, will not take effect immediately and will go through a regulatory process to allow public comment for 30 days before the policy is finalized. After that time, the policy is set to be in place for two years following its effective date.

The effort is the latest Biden administration proposal to deter migrants from entering the U.S. without authorization, and to bring down the numbers of migrants crossing the southern border. The policy is being unveiled as the administration prepares for the expected end in May of Title 42, a Trump-era policy that allows border agents to quickly turn back migrants at the border.

The government had struggled to lower the number of crossings at the border before it decided to expand its use of Title 42 in January to expel Nicaraguans, Haitians, Venezuelans and Cubans to Mexico. At the same time, the Department of Homeland Security allowed immigrants from those countries who had verified sponsors in the country to enter the U.S. legally. Following the announcement, the numbers of unauthorized border crossings went down in January to their lowest levels in almost two years.

“We will sue if this administration goes through with a transit ban, just as we successfully sued over the Trump transit ban,” said Lee Gelernt, a senior attorney with the ACLU.

Since Biden administration officials hinted at the effort in January, advocates have criticized the idea, saying it mirrors Trump’s move to block asylum for those who crossed into the U.S. without authorization and did not seek protections in another country on their journey. That proposal was later blocked in federal court.

“The Biden administration must adjust course immediately and abandon the misguided pursuit of an asylum ban. We urge you not to issue the [proposal] on the asylum ban,” a group of nearly 300 immigrant advocacy groups wrote to the Biden administration in a January letter.

Biden administration officials, however, have said this policy is not comparable because it does not categorically ban asylum.

Under the proposal, immigrants who do not seek legal pathways into the U.S., schedule a time to arrive at a port of entry or seek and are denied asylum in a separate country on their way to the U.S. would be forced to overcome a presumption that they are ineligible for asylum.

Immigrants who do not overcome that hurdle would be deported unless they meet one of several exceptions included in the policy, or clear a higher bar for protection in the U.S. Asylum officers are expected to handle interviews of immigrants crossing the U.S. border.

Exceptions include experiencing a medical emergency, an imminent threat to life or victimization from a severe form of trafficking.

A record number of migrants descended on the Southwest border last year, putting political pressure on the Biden administration. Border agents made more than 2 million arrests at the border during the yearlong period that ended Sept. 30, 2022, according to Customs and Border Protection data. Republicans have argued those numbers prove Biden is weak on border security.

Biden has sought to end Title 42 but has faced legal challenges from Republican-led states who argue ending the policy would result in a surge of migrants to the U.S.-Mexico border. The Supreme Court ordered the administration to keep the policy in place until it rules on the states’ lawsuit.

The administration, however, plans to allow the public health emergency for COVID-19 that underlies Title 42 to expire on May 11. Following that announcement, the Supreme Court took arguments scheduled in the case off its docket.

Despite the administration’s effort to end Title 42, in recent months officials have expanded its use by turning back Venezuelans, Cubans, Nicaraguans and Haitians to Mexico under the policy, limiting the ability of thousands of migrants to seek asylum. Mexico has agreed to allow U.S. officials to return up to 30,000 migrants per month.

Before January, Venezuelan and Cuban migrants for the most part had been able to cross the border and seek protections. The U.S. had been unable to deport migrants at high levels from those countries as well as Nicaragua due to strained relations with their governments.

The Biden administration has said the U.S. is facing an unprecedented surge in migration in the Western Hemisphere, including from Venezuela. That country has seen almost 7 million people leave since 2014.