The ACLU and other immigration advocates have sued to block the Trump administration's controversial immigration policy that forces some asylum seekers to stay in Mexico while they wait for their day in immigration court.

A federal judge heard arguments Friday, and a decision on a preliminary injunction could come as soon as Monday.

Lee Gelernt, an attorney for the ACLU, told CBS News that the judge was "extremely well-prepared" and "recognized that there was virtually no process afforded to the people who were sent back. There's no question that he understood how little [due] process people are getting, and the stakes that are involved."

The case involves the Department of Homeland Security's new "Migrant Protection Protocol" initiative. The policy — which Mr. Trump dubbed "Remain in Mexico" when it was announced in December — was implemented at the end of January in San Diego.

Under the policy, more than 250 migrants seeking asylum have been returned to Mexico. It applies to "aliens arriving in the U.S. on land from Mexico (including those apprehended along the border) who are not clearly admissible and who are placed in removal proceedings," according to a fact sheet from DHS in January. Unaccompanied children are not subject to the program.

The American Immigration Lawyers' Association has called the policy a "due process disaster."

Advocates worry about safety in Tijuana, a dangerous city where many asylum seekers have been sent. In a filing for the lawsuit, Katie Sheppard, the national advocacy Counsel for the Immigration Justice Campaign at the American Immigration Council, noted that 2,518 murders occurred in the border city last year, nearly seven times the total in 2012. At least one shelter in the city has begun receiving death threats for hosting the migrants, said Robyn Barnard, a Los Angeles-based immigration attorney who's representing two clients that have been subject to "Remain in Mexico."

The program initially applied to asylum seekers in San Ysidro, a district in San Diego, and has expanded to El Paso and Calexico.

The ACLU, SPLC and Center for Gender and Refugee Studies, filed a lawsuit against the policy in February, claiming that "Remain in Mexico" was in violation of the Immigration and Nationality Act, the Administration Procedures Act, and various international human rights law that the United States is subject to. The lawsuit, Innovation law Lab v. Nielsen, represents 11 asylum seekers and six organizations impacted by the policy shift.

The case is being heard by Judge Richard Seeborg in the Northern District of California.

"While the Trump administration continues to double down on this policy by expanding its implementation, the irreparable harm it causes is clear," said Melissa Crow, a senior supervising attorney for the Southern Poverty Law Center who argued the case. "Every moment it is in place, it jeopardizes the lives and well-being of vulnerable asylum seekers and makes it virtually impossible for them to present their cases in court. It is inhumane and unlawful"