A Chinese university is investigating allegations that its professors stole tech secrets from the U.S., but the school is so far skeptical of the claims.

“This could be a U.S. fabrication,” a school staff member said Wednesday.

On Tuesday, the U.S. Department of Justice charged six Chinese nationals with economic espionage, for allegedly stealing wireless technologies used in mobile devices. All six are connected with Tianjin University, about 90 miles southeast of Beijing.

One of those named, Tianjin University Professor Hao Zhang, was arrested in the U.S. four days ago. The other five remain at large.

Tianjin University is investigating the claims, and only learned about the charges on Wednesday from media reports, said a school staff member surnamed Song who works in its media relations department.

Although the university has given no official statement, Song said the U.S. has accused Chinese nationals of spying before, only to drop the accusations later.

“These types of cases have been happening more,” Song added. “The U.S. is paying greater attention to cybersecurity. But the U.S. has also shown a double standard in this area.”