Former cabinet minister Clare Short says she has received "a threatening letter" from the head of the civil service telling her to stop making claims about Britain's spies.
Clare Short said Sir Andrew had allowed Britain "to rush to war"
She said Cabinet Secretary Sir Andrew Turnbull warned her not to give interviews about claims that Britain bugged the UN Secretary General.
She said the letter spoke of action being taken against her.
The government says it was his duty to remind her of her obligations.
In a confidential letter, Sir Andrew said he was "extremely disappointed" that she saw fit to make claims which damaged the country's interests and he reserved the right of the Crown to take "any further action as necessary".
But Ms Short defended her right to speak out saying: "So much smearing is going on I just want to give my account of events."
A Downing Street spokeswoman said it was the duty of the cabinet secretary to remind ministers and ex-ministers of the obligations they accepted when taking up office.
Ms Short also accused Sir Andrew of allowing Britain to "rush to war" without the proper preparations.
"He allowed us to rush to war in Iraq without defence and overseas policy
meeting, looking at all the military options and the diplomatic options and
Lord Goldsmith advised the PM before the Iraq war
(He) allowed the Joint Intelligence Committee to meet with
Alastair Campbell chairing it. He has allowed our decision making system to
Ms Short also questioned the impartiality of the Attorney General, Lord Goldsmith, who advised Tony Blair about the legality of going to war in Iraq.
Her latest attack comes as Tony Blair faces pressure to publish the attorney general's advice.
On Sunday former Tory Prime Minister John Major added his voice to calls for the full advice to be made public.
He told the BBC it was in the prime minister's interests to release the full advice as further speculation would damage the government further.
Downing Street had earlier refused to comment on newspaper reports that the attorney general changed his advice shortly before the allied campaign began.
Ms Short said there had been unease across Whitehall over the legality of the war without a second UN resolution.
Then "right at the last minute", Lord Goldsmith went to the cabinet with a brief statement saying there was legal authority.
"It is hard not to think he (Lord Goldsmith) may have been leant on," she said.
Ms Short pointed out Lord Goldsmith is "a friend of Tony's" and Mr Blair put him in the Lords as well as making him attorney general.
Earlier on Sunday Alastair Campbell talked to London's LBC News about Ms Short's claims.
"I think it's very sad that people who have been in position of influence and authority now behave in a way that just reveals a bitterness that is very very deep.
"I'm not going to waste too much breath on her. I just think people feel sad when people they may well have respected behave in away that is clearly very very bitter."