Grand jury subpoenas have been sent to Bolton's publisher, Simon and Schuster, and his literary agent, Javelin, demanding they hand over their communications with Bolton, the sources confirmed. The convening of a federal grand jury does not necessarily mean that Bolton will ultimately face criminal charges as a result of the investigation.
“We are aware of reports that grand jury subpoenas have been issued seeking information concerning the publication of Ambassador Bolton‘s recent book," Bolton's lawyer Chuck Cooper said in a statement. "Ambassador Bolton emphatically rejects any claim that he acted improperly, let alone criminally, in connection with the publication of his book, and he will cooperate fully, as he has throughout, with any official inquiry into his conduct.”
A Justice Department spokeswoman declined to comment. Simon and Schuster declined to comment and Javelin did not immediately respond to a request for comment from ABC News.
The news was first reported by The New York Times and Wall Street Journal.
The DOJ already has an ongoing civil suit against Bolton seeking the proceeds from his book after it failed in June to secure a court order blocking its release on grounds that Bolton's disclosures posed potentially grave consequences for national security.
The federal judge overseeing that case, however, Royce Lamberth, issued a ruling that spelled trouble for Bolton stating that he agreed with the government's argument that the book contained highly classified material -- essentially paving the way for the government to possibly charge Bolton criminally under the Espionage Act.
"This was Bolton’s bet: If he is right and the book does not contain classified information, he keeps the upside... but if he is wrong, he stands to lose his profits from the book deal, exposes himself to criminal liability, and imperils national security. Bolton was wrong," Lamberth said.
Bolton's attorney has argued that the pre-publication review of Bolton's book was unfairly politicized by the White House after he was initially informed by an NSC official Ellen Knight that she had finished the review of his book and "was of the judgment that the manuscript draft did not contain classified information." Soon after, however, Bolton was informed that the review was still ongoing and that a separate NSC official determined it still contained passages with classified information.
"In fact, the NSC has determined that information in the manuscript is classified at the Confidential, Secret, and Top Secret levels," department attorneys said in a June court filing.
The criminal investigation of Bolton will likely draw skepticism from critics who have alleged Attorney General William Barr has bent the nation's top law enforcement agency to advance the interests of President Donald Trump.
Trump has repeatedly called for Bolton's prosecution amid coverage of the damning revelations in Bolton's book and cheered on the DOJ's ultimately unsuccessful attempt to force his publisher to stop its release.
Barr has denied the Justice Department had any political motivations in bringing its case against Bolton.