Rob Evans, a Guardian journalist, submitted a freedom of information request to see the letters but this was denied by the information commissioner.

BBC: Prince Charles letters to government must be published

The USA PATRIOT Act expanded the purpose of National Security Letters (NSL) to allow government agencies to use them to request any data relevant to an investigation of terrorism or an intelligence activity without court oversight.

FORBES: The Sheep Stop Here: Another Church Committee or Full Review of Privacy Laws Needed?

When I review institutional portfolios, I regularly request, receive and review non-public SEC deficiency letters of firms handling client assets.

FORBES: SEC Conceals Far More Crime Than You Ever Imagined

The FDA replied to a request for comment with three letters: "FOI, " referring to the Freedom of Information Act.

FORBES: The FDA's Conflict Of Interest Problem