Glassdoor Inc., the operator of the anonymous online job review site, has asked the U.S. Court of Appeals for the Ninth Circuit to block an attempt by federal prosecutors to unmask reviewers as part of a grand jury investigation.

In a case unsealed on Tuesday, Glassdoor was ordered by U.S. District Judge Diane Humetewa for the District of Arizona to divulge the identities of eight people who posted anonymous reviewers about a federal contractor under investigation for fraud.