A federal appeals court ruled on Wednesday that a key aspect of the mass surveillance program exposed by former National Security Agency contractor Edward Snowden was illegal, but it did not reach a conclusion on its constitutionality.

A three-judge panel on the U.S. Court of Appeals for the 9th Circuit also upheld the convictions of four men who said they were monitored under the program for sending thousands of dollars to support the terrorist group al Shabab back in Somalia.