A federal appeals court on Tuesday ruled that the Trump administration can for now continue returning Central American migrants to Mexico while their requests for asylum in the U.S. are adjudicated, a boost for White House efforts to tighten the southern border.

The decision by the San Francisco-based Ninth U.S. Circuit Court of Appeals is a surprise victory for the administration, which previously had been on the losing end of several immigration-related rulings by the liberal-leaning court.

The ruling stays the effect of a decision by a federal trial judge who last month blocked the policy while it is being challenged in court.

The policy, officially named the Migrant Protection Protocols, is more commonly known as “Back to Mexico” or “Remain in Mexico.”

While Tuesday’s court action isn’t a final decision on the merits of the case, the appeals court held that several legal factors favored allowing the Trump administration to administer the policy while the litigation continues.