President Donald Trump’s administration is pursuing a rule that would drastically reduce Central American migrants’ ability to seek asylum in the U.S., although critics have promised legal challenges that might dilute the impact.

The new rule, which was published in the Federal Register and is set to take effect on Tuesday, makes people ineligible for asylum at the southern border of the U.S. if they have passed through another country first without applying for protection there. Among others, that would cover Central American migrants who travel through Mexico before arriving at the U.S. but don’t seek asylum from Mexico.

The policy attracted criticism from Democratic Sen. Jacky Rosen, who vowed to continue working across the aisle on comprehensive immigration reform.

“Let’s be clear: there is nothing illegal about seeking asylum. Yet this Administration continues to ignore our laws and effectively end asylum for migrant families who are risking their lives fleeing persecution and violent circumstances in their home countries and in search for safety,” she said in a statement on Monday. “We must treat all immigrants with the dignity and compassion that represent our American values.”

Supplementary materials to the rule say the government has seen a sharp increase in the number of immigrants seeking asylum when they encounter Immigration and Customs Enforcement (ICE) or the Border Patrol. In the past decade, the document says, the percentage of immigrants subject to an expedited deportation who have been referred to asylum proceedings has jumped from 5 percent to 40 percent.

“Only a small minority of these individuals, however, are ultimately granted asylum,” the document says. “The large number of meritless asylum claims places an extraordinary strain on the nation’s immigration system, undermines many of the humanitarian purposes of asylum, has exacerbated the humanitarian crisis of human smuggling, and affects the United States’ ongoing diplomatic negotiations with foreign countries.”

The rule, according to the government, “mitigates the strain on the country’s immigration system by more efficiently identifying aliens who are misusing the asylum system.”

Professor Michael Kagan, who leads the Immigration Clinic at UNLV, said that while the number of border crossings is not at its historical high, there have been a high number of children and families seeking entry into the U.S. He said the mix of immigrants has shifted from single adults seeking work, often from Mexico, toward more children and families fleeing violence and instability in Central America.

The rule unveiled Monday, he said, could have a devastating impact if it takes full effect.

“It could really end much of the U.S. asylum system as we know it,” he said.  

But as with other rules the administration has proposed, some take effect and some are halted through court proceedings.

Kagan also noted that while asylum is the protection that affords the most benefits, including a path to citizenship, people fleeing violence could also apply for less comprehensive protections known as “withholding of removal” or “Protection Under Convention Against Torture” 

The rule is part of a larger package of policies, both formal and informal, aimed at curtailing the use of asylum, Kagan said. Another example is “metering,” in which asylum seekers wait sometimes weeks in Mexico for their names to be called so they can be processed.

“It used to be something that America was proud of — that we had one of the most developed asylum systems in the world,” Kagan said. “The current government maybe sees that as a liability.”

In 2017, U.S. Citizenship and Immigration Services (USCIS) received 139,801 asylum applications — a number that had been growing for eight straight years. The government granted asylum in 26,568 cases that year.