At least 21 news organisations, including CNN, the New York Times, and Associated Press, are to ask an appeal court panel to nullify the right of "Real IRA" leader, Michael McKevitt, to seize copies of US journalists' interviews with FBI informant, Mr David Rupert.
A three-judge appeal court in the US ruled earlier this month that McKevitt had the right to subpoena the interview tapes for use in his unsuccessful defence at a trial at the Special Criminal Court in Dublin on charges of directing terrorism.
However, most of the major news organisations in the US are expected to file a joint "friends of the court" brief on Friday in which they will call for a full hearing of the case by at least 11 judges on the Seventh Circuit Appeal Court in Chicago.
Under federal law, an appellant whose case is turned down by a three-judge appeal court can apply to have the case reheard by the entire bench of appeal judges on that circuit.
The media organisations, which include Time magazine, the New York Times, Turner Broadcasting, NBC, the Los Angeles Times, CBS, Hearst Newspapers, Fox News and the Washington Post, are to argue that the appeal court decision sets a precedent that will greatly hinder the media's right to freedom of expression, guaranteed under the US constitution.
Many of the organisations fear that witnesses such as Mr Rupert would refuse to speak to the media if their words could be used against them in court.
A New York media attorney organising the briefing, Mr Victor Kovner, listed 21 news organisations whose legal teams were helping to write the wording of the submission, and said he would most likely lodge the brief in a Chicago court on Friday.
"Some of the 21 entities involved covered many different publications so this is a very significant portion of the national press in the US. People are very interested in this," he said.
Mr Kovner said that his firm, Davis, Wright and Tremaine, had contacted each news organisation individually and had a very enthusiastic response.
Earlier this month, the Seventh Circuit Appeal Court unanimously rejected the concept that the journalists in the McKevitt case had a greater right to protect their sources than other members of the public.