The letters warn special operators that they may come under public scrutiny or be contacted by media, and are offered resources on how to deal with the response, said Naylor, a contributing editor at Foreign Policy magazine.

They are also "reminded not to talk about the content of the book in any way, shape or form," he added.

Naylor said he's been told that Fort Bragg, where the U.S. Army's Special Operations Forces is headquartered, "is going ape shit over your book."

In response to a query about whether the letters exist, the Special Operations Command told The Hill, "In general, USSOCOM reminded its personnel that they must follow the same protocols that govern sensitive material regardless of whether or not the information has been publicly released, and they are still bound by any nondisclosure agreements they signed."

"Aside from that, it would be inappropriate for us to comment further until we have had the opportunity to fully review the book," added Lt. Col. Robert Bockholt, the chief of media, plans and operations for USSOCOM.

Naylor, who previously covered special operations forces for Army Times, said he was not passed any classified documents for the book, or to his knowledge, given any classified information.

Nonetheless, the book has garnered the attention of top Pentagon leadership, which has struggled to keep a lid on information of special operations forces at a time when more operators have written books or spoken out about their experiences.

Many blame administration officials for first selectively condoning some movies or allowing defense officials to speak off the record or on background about high-profile operations.

Defense Secretary Ashton Carter became the latest Pentagon official to issue a warning on Friday.

"Obviously, it's not up to any individual who is entrusted with national security secrets to disclose them ... and especially when it would affect the ability to protect our people and our country, our compromised secrets," Carter told Defense One on Friday, when asked about the book.

The book's subject, Joint Special Operations Command, or JSOC, is a subdivision of USSOCOM made up of Navy SEALs, Delta Force and other special operators, tasked with the most secret and sensitive of missions, such as the 2011 raid that killed Osama bin Laden.