A federal appeals court is giving the Federal Bureau of Investigation a big boost when it comes to secretly investigating national security affairs. The 9th US Circuit Court of Appeals on Monday upheld federal rules prohibiting companies from promptly disclosing to customers that the FBI is demanding a user’s private data with a National Security Letter (NSL).

The FBI annually issues thousands of so-called NSLs to ISPs, financial institutions and telephone companies. A judge’s signature is not required, and targets of NSLs cannot challenge them because they don’t know they exist.

The Electronic Frontier Foundation, on behalf of Cloudfare and CREDO Mobile, brought a challenge to the gag orders under the First Amendment. They argued that the gag orders burdened the speech of companies that receive them. A federal judge in 2013 agreed, and declared NSLs unconstitutional for that reason.