Risen has been called to testify against Jeffrey Sterling, who the government says gave Risen classified information that he used in his book "State of War." The government has argued that Risen could testify about his previous relationship with Sterling without violating any confidentiality agreement with the former CIA agent.
But he wrote that he had found that the government "all too frequently" claims disclosure of certain information would harm national security, "when in reality, the government's real concern is about covering up its own wrongdoing or avoiding embarrassment."
Risen accused the Obama administration of continuing an effort to intimidate him that started during the Bush era.
"By publicly speculating about the possibility of prosecuting journalists, such as myself, under the Espionage Act for publishing truthful stories containing classified information, I believe that the Government was trying to intimidate journalists, like me, who publish stories that expose excessive government secrecy, illegality, or malfeasance," Risen wrote.
"I believe that the efforts to target me have continued under the Obama Administration, which has been aggressively investigating whistleblowers and reporters in a way that will have a chilling effect on the freedom of the press in the United States," he continued.
Risen says his promise of confidentiality is essential to his reporting.
"In my ongoing reporting and news gathering, numerous sources of confidential information have told me that they are comfortable speaking to me in confidence specifically because I have shown that I will honor my word and maintain their confidence even in the face of Government efforts to force me to reveal their identities or information," Risen writes.
"The fact that I have not previously revealed my sources has allowed me to gain access to newsworthy information that I could not otherwise get," he continues.