Immigrant and human rights advocates filed a motion Thursday in an ongoing legal battle seeking to block the Trump administration from applying its most stringent asylum restriction to some migrants who were forced to wait after coming to a port of entry on the southern border.

The new filing spans from a 2-year-old lawsuit challenging the Trump administration’s attempts to turn back asylum-seekers who present themselves at ports of entry along the United States-Mexico border. Among the tactics being targeted by the lawsuit is the use of “metering,” or limiting the number of migrants who can enter at a port of entry per day.

But the new filing centers around the Trump administration’s toughest restriction yet, the July policy of refusing to consider the vast majority of requests for asylum from any migrant who failed to apply for it in another country after leaving their home and before coming to the U.S.

Migrants who were forced to wait in Mexico because of metering prior to that policy’s announcement have been unfairly denied their right to seek asylum in the U.S., the Southern Poverty Law Center, the Center for Constitutional Rights, the American Immigration Council and plaintiff Al Otro Lado said as they announced the motion in a news teleconference Thursday morning.

The groups were in the process of filing a motion for a preliminary injunction “for individuals who were metered prior to July 16 who but for the government’s illegal use of metering would have entered the United States before the asylum ban went into effect,” Melissa Crow, senior supervising attorney for the SPLC’s Immigrant Justice Project, said.

“We’re asking the court to block the government from applying the ban to this group of people who followed all the rules the U.S. government imposed but were still unable to access the asylum process because the rug was pulled out from under them,” she said.

Earlier this month, the Supreme Court ruled the government could enforce the policy of effectively barring migrants from seeking asylum if they did not seek relief in another country on their journey first as a lawsuit seeking to stop the policy plays out in court.

The administration has said the new restriction is needed to respond to the "ongoing crisis" of people coming to the U.S. border and to mitigate the strain on the country’s backlogged immigration system. Officials have also said they want to crack down on asylum claims without merit.

The government has previously defended metering, citing capacity limits.

There were currently about 26,000 migrants waiting in Mexican border towns to seek asylum who have been turned away from ports of entry, Crow said Thursday, many of them stuck in overcrowded shelters and potentially dangerous conditions for months.

The motion could prevent the Trump administration from applying the third-country restriction to “hundreds and potentially thousands of class members who face the illegality of the asylum ban only because of the illegality of the metering policy,” Baher Azmy, legal director at the Center for Constitutional Rights, said.

“Had the government not put people unlawfully on endless waitlists and otherwise denied them access to the asylum process, they would have been processed,” he said.

The groups are asking the court to decide on the motion by Oct. 21.