A Washington grand jury, investigating the disclosure of the name of a CIA undercover agent, has summoned New York Times reporter Judith Miller, but the newspaper said Friday it would fight the order.
A Washington judge has already held Time magazine journalist Matthew Cooper in contempt for refusing to divulge his sources in the same case.
"We regret that the special prosecutor has chosen to issue a subpoena that seeks to compel Judy Miller to reveal her confidential sources," said New York Times publisher Arthur Sulzberger was quoted as saying in the newspaper.
"Journalists should not have to face the prospect of imprisonment for doing nothing more than aggressively seeking to report on the government's actions," added the executive.
"Such subpoenas make it less likely that sources will be willing to talk candidly with reporters and ultimately it is the public that suffers."
Special prosecutor Patrick Fitzgerald has summoned several journalists to give evidence in the investigation over the leaking last year of the name of CIA agent Valerie Plame, the wife of Joseph Wilson, an outspoken critic of the Iraq war.
An investigation was launched to see if the White House was at the centre of the leak. It is illegal in the United States to reveal the names of CIA operatives.
The case has become a new battle in journalists' attempts to protect sources since Cooper was ruled in contempt by federal judge Thomas Hogan after he refused to give details of his source.
Time magazine has been ordered to pay 1,000 dollars each day that the journalist maintains his refusal. Cooper and Time have launched appeals and the court put their penalties on hold while the appeals progress.