Washington (CNN) Acting Customs and Border Protection Commissioner Mark Morgan on Thursday said a new asylum rule introduced earlier this week is in the "piloting" phase even as officials expect it to be blocked in court.

"Although the new federal regulation allows us to apply that all 2,000 miles along the southwest border, we're not going to do that. We're really piloting it in just one location," Morgan told NPR's All Things Considered . The regulation is being rolled out at two CBP stations in the Rio Grande Valley, he said.

The American Civil Liberties Union and other groups have sued the Trump administration to block the restrictions. A hearing is scheduled next week in federal court in California.

The asylum rule from the Departments of Justice and Homeland Security would -- with limited exceptions -- prohibit migrants who have resided or "transited en route" in a third country from seeking asylum in the US, therefore barring migrants traveling through Mexico from being able to claim asylum and as a result, drastically limit who's eligible for asylum.

The asylum workforce was notified of the changes late Monday night, and did not suggest that it was in a pilot phase.

"Until Congress can act, this interim rule will help reduce a major 'pull' factor driving irregular migration to the United States," acting Homeland Security Secretary Kevin McAleenan in a statement Monday. "It will allow the departments of Justice and Homeland Security to "more quickly and efficiently process cases originating from the southern border, leading to fewer individuals transiting through Mexico on a dangerous journey."

Lee Gelernt, deputy director of the Immigrants' Rights Project of the ACLU, called the rule "patently unlawful" in a statement Monday

"The Trump administration is trying to unilaterally reverse our country's legal and moral commitment to protect those fleeing danger. This new rule is patently unlawful and we will sue swiftly," the statement said.