According to a proposed regulation unveiled on Tuesday, the Biden administration may prevent tens of thousands of migrants from seeking asylum if they traveled through another nation on their way to the United States without doing so, according to five people who spoke to Reuters.

The proposed limitations would represent U.S. President Joe Biden’s most extensive effort to date to discourage border crossings without authorization. Biden, who is anticipated to run for re-election in 2024, has had a difficult time adjusting to the record-breaking influx of new immigrants.

Under the new rules, migrants who fail to use existing legal pathways to the United States or seek protection in transit would automatically be considered ineligible for asylum unless they qualify for certain exceptions, the U.S. Department of Homeland Security (DHS) said in January.

The rule, to be announced later on Tuesday, will be subject to a 30-day public comment period and then reviewed before final publication, three of the sources said.

Biden, a Democrat who took office in 2021, initially pledged to restore asylum access that was curtailed under his Republican predecessor, Donald Trump. But advocates and some fellow Democrats have criticized him for increasingly embracing Trump-style restrictions.

Biden’s plan to ban certain asylum seekers mirrors similar efforts under Trump that were blocked by federal courts.

Families and single adults will be subject to the restrictions while unaccompanied minors will be exempt, three sources familiar with the matter said, requesting anonymity to discuss the not-yet-public proposal.

The rule will be time-limited to a period of two years, two of the sources said.

The American Civil Liberties Union (ACLU) vowed to fight the Biden rule in court, comparing it to the Trump restriction, which was dubbed a “transit ban” by activists.

“We successfully sued to block the Trump transit ban and will sue again if the Biden administration goes through with its plan,” said Lee Gelernt, the ACLU attorney who argued the Trump-era lawsuit.

The ban and other Trump-style policies were being discussed by the Biden administration last year as a means to curb illegal crossings in the event that COVID-era limits allowing many migrants to be sent back to Mexico were lifted. As the COVID limits, also known as Title 42, are likely to expire on May 11 when the COVID-19 public health emergency ends, the administration is pressing forward with tighter asylum regulations.

According to a person involved with the planning, “this was neither our first priority nor our second preference.” The White House is pleading with Congress to either adopt comprehensive immigration reform or increase funds for border security.

An inquiry for comments was not immediately answered by Mexican officials.