Yahoo published three secret requests for user information from the FBI on Wednesday. It marked the first time the FBI has allowed a company to tell the public it received National Security Letters based on a process set up in last year's USA Freedom Act, Yahoo said.

The letters are special subpoenas issued by the FBI requiring companies to hand over all kinds of information about a user's accounts. This includes metadata -- or all the records of who a user emailed and chatted with and when -- as well as any addresses, telephone numbers and screen names associated with the user's account. The subpoenas are not reviewed by a judge outside of the FBI.

"We believe this is an important step toward enriching a more open and transparent discussion about the legal authorities law enforcement can leverage to access user data," wrote Yahoo Associate General Counsel Chris Madsen in a blog post on Wednesday.

The USA Freedom Act became law in June 2015. It increased oversight in the government's surveillance programs and curtailed some of the broad governmental powers endowed by the Patriot Act.

"Yahoo recently received notice from the FBI that it was no longer under an obligation not to disclose the NSL," an FBI representative said in an email Wednesday. "This notice was the result of the FBI's review under its Termination Procedures for NSL Nondisclosure Requirements."

Companies are restricted from telling anyone about National Security Letters, including the users targeted by the FBI. With the passage of the USA Freedom Act, the FBI is now required to review these restrictions periodically, as it did with Yahoo, to decide if they're still crucial to national security.

The user names are redacted from the three letters published on Wednesday by Yahoo, but the company notified them privately.