A federal judge decided on Wednesday not to block the Trump administration’s latest restriction on asylum requests by migrants fleeing violence in their home countries.

Judge Timothy J. Kelly of D.C. upheld the administration’s proposed rule, which was challenged on July 16 in a lawsuit brought by several migrant advocacy groups. Under the new rule, asylum-seekers who pass through another country on their way to the U.S. will be denied entry here, unless they were already rejected for asylum in that third country.

It constitutes the most severe step taken by the Trump administration thus far to curtail asylum requests. It’s going to disproportionately impact people from Central American countries like El Salvador and Honduras—the majority of those seeking asylum on the southern U.S. border—as they have all passed through at least one other country, Mexico, on their way to the United States.

This rule comes after President Donald Trump’s attempts to negotiate bilateral “safe third country” agreements with Mexico and Guatemala recently collapsed.

The U.S. currently has a deal along these lines with Canada, stipulating that migrants must apply for asylum in whichever of those two countries they reach first. But when the president approached Mexican and Guatemalan leaders with the proposal that they become designated “safe third countries,” he was rebuffed by Mexico and put on hold in Guatemala.

In response, the administration decided to forgo any agreement and stipulated that migrants will have to apply for asylum in whichever country they reach before coming to the U.S., regardless of the dangers they might face there.

The Trump administration has framed this rule as an attempt to make illegal immigration less appealing to those fleeing Central America, thereby discouraging immigrants from undertaking dangerous journeys through Mexico.

The two nonprofits challenging the rule in court—the Capital Area Immigrants’ Rights Coalition and the Refugee and Immigrant Center for Education and Legal Services—argued that it violated the Immigration and Naturalization Act as well as the Administrative Procedure Act. The plaintiffs said that these acts stipulate that once asylum-seekers reach the U.S., they are allowed to apply for refuge.

Kelly, who was appointed by Trump, said that “I’m not sure it would cause no irreparable harm” to migrants if this rule was implemented. Still, he maintained that he ruled in favor of the policy because the immigrants’ rights groups could not quantify how many asylum-seekers would be turned away and how many would be accepted into the country as a result.

Although this suit has now been struck down, the American Civil Liberties Union has brought another lawsuit in San Francisco, where a judge is going to hear arguments on Wednesday.