Donald Trump has revoked the security clearance of ex-CIA chief John Brennan, denying the US president's critic any access to sensitive information.
White House press secretary Sarah Sanders announced the decision by reading a statement from Mr Trump.
The statement cited Mr Brennan's "erratic conduct and behaviour".
In response, Mr Brennan tweeted that the move was part of President Trump's broader effort to "suppress freedom of speech and punish critics".
"It should gravely worry all Americans, including intelligence professionals, about the cost of speaking out.
"My principles are worth far more than clearances. I will not relent."
Mr Brennan earlier said Mr Trump's performance at a briefing after July's summit with Russian President Vladimir Putin in Helsinki had been "nothing short of treasonous".
And last year, Mr Brennan said an investigation into possible collusion between Trump campaign officials and Russia during the US presidential elections in 2016 had been "well-founded".
President Trump has repeatedly denied the claim, calling it "witch hunt".
Later on Wednesday in an interview with the Wall Street Journal, Mr Trump said he would have revoked Mr Brennan's clearance last week but it was "too hectic".
What did Trump's statement say exactly?
"As the head of the executive branch and commander-in-chief, I have a unique constitutional responsibility to protect the nation's classified information, including by controlling access to it.
"I have decided to revoke the security clearance of John Brennan, former director of the Central Intelligence Agency.
"Historically, former heads of intelligence and law enforcement agencies have been allowed to retain access to classified information after their government service so that they can consult with their successors, regarding matters about which they may have special insights and as a professional courtesy.
"Neither of these justifications supports Mr Brennan's continued access to classified information."
The statement added that Mr Trump was also reviewing access to classified information for former FBI chief James Comey, whom he fired last year, former director of national intelligence James Clapper, former National Security Agency director Michael Hayden and former attorney general Sally Yates, among others.