The Justice Department secretly obtained two months of telephone records of reporters and editors for The Associated Press in what the news cooperative’s top executive called a “massive and unprecedented intrusion” into how news organizations gather the news.

The records obtained by the Justice Department listed outgoing calls for the work and personal phone numbers of individual reporters, for general AP office numbers in New York, Washington and Hartford, Conn., and for the main number for the AP in the House of Representatives press gallery, according to attorneys for the AP. It was not clear if the records also included incoming calls or the duration of the calls.

In all, the government seized the records for more than 20 separate telephone lines assigned to AP and its journalists in April and May of 2012. The exact number of journalists who used the phone lines during that period is unknown, but more than 100 journalists work in the offices where phone records were targeted, on a wide array of stories about government and other matters.

In a letter of protest sent to Attorney General Eric Holder on Monday, AP President and Chief Executive Officer Gary Pruitt said the government sought and obtained information far beyond anything that could be justified by any specific investigation. He demanded the return of the phone records and destruction of all copies.

“There can be no possible justification for such an overbroad collection of the telephone communications of The Associated Press and its reporters. These records potentially reveal communications with confidential sources across all of the newsgathering activities undertaken by the AP during a two-month period, provide a road map to AP’s newsgathering operations and disclose information about AP’s activities and operations that the government has no conceivable right to know,” Pruitt said.

The government would not say why it sought the records. Officials have previously said in public testimony that the U.S. attorney in Washington is conducting a criminal investigation into who may have provided information contained in a May 7, 2012, AP story about a foiled terror plot. The story disclosed details of a CIA operation in Yemen that stopped an al-Qaida plot in the spring of 2012 to detonate a bomb on an airplane bound for the United States.

In testimony in February, CIA Director John Brennan noted that the FBI had questioned him about whether he was AP’s source, which he denied. He called the release of the information to the media about the terror plot an “unauthorized and dangerous disclosure of classified information.”

Prosecutors have sought phone records from reporters before, but the seizure of records from such a wide array of AP offices, including general AP switchboards numbers and an office-wide shared fax line, is unusual.

In the letter notifying the AP, which was received Friday, the Justice Department offered no explanation for the seizure, according to Pruitt’s letter and attorneys for the AP. The records were presumably obtained from phone companies earlier this year although the government letter did not explain that. None of the information provided by the government to the AP suggested the actual phone conversations were monitored.

Among those whose phone numbers were obtained were five reporters and an editor who were involved in the May 7, 2012, story.

The Obama administration has aggressively investigated disclosures of classified information to the media and has brought six cases against people suspected of providing classified information, more than under all previous presidents combined.

The White House on Monday said that other than press reports it had no knowledge of Justice Department attempts to seek AP phone records.

“We are not involved in decisions made in connection with criminal investigations, as those matters are handled independently by the Justice Department,” spokesman Jay Carney said.

Rep. Darrell Issa, R-Calif., chairman of the investigative House Oversight and Government Reform Committee, said on CNN, “They had an obligation to look for every other way to get it before they intruded on the freedom of the press.”

Sen. Patrick Leahy, D-Vt., chairman of the Senate Judiciary Committee, said in an emailed statement: “The burden is always on the government when they go after private information, especially information regarding the press or its confidential sources. … On the face of it, I am concerned that the government may not have met that burden. I am very troubled by these allegations and want to hear the government’s explanation.”

The American Civil Liberties Union said the use of subpoenas for a broad swath of records has a chilling effect both on journalists and whistle-blowers who want to reveal government wrongdoing. “The attorney general must explain the Justice Department’s actions to the public so that we can make sure this kind of press intimidation does not happen again,” said Laura Murphy, the director of ACLU’s Washington legislative office.

Rules published by the Justice Department require that subpoenas of records of news organizations must be personally approved by the attorney general, but it was not known if that happened in this case. The letter notifying AP that its phone records had been obtained through subpoenas was sent Friday by Ronald Machen, the U.S. attorney in Washington.

William Miller, a spokesman for Machen, said Monday that in general the U.S. attorney follows “all applicable laws, federal regulations and Department of Justice policies when issuing subpoenas for phone records of media organizations.” But he would not address questions about the specifics of the AP records. “We do not comment on ongoing criminal investigations,” Miller said in an email.