Scotland Yard is trying to force the Guardian newspaper to reveal who told it the mobile phone of a murdered schoolgirl had been hacked by News of the World reporters.
The Guardian ran the story in July and the resulting scandal, led to the paper's closure.
The Guardian said it would resist the "unprecedented legal attack".
The Metropolitan Police said it was probing potential Official Secrets Act breaches and misconduct and not trying to stop investigative journalism.
It confirmed it had applied for a production order against the Guardian and one of its reporters.
The paper reported on Friday that the Metropolitan Police claiming that the Official Secrets Act could have been breached in relation to the original article on the hacking of the dead girl's mobile phone voicemail.
The paper said that police were due to go to the Old Bailey in London on 23 September, in an attempt to force the handover of documents relating to sources for a number of articles.
The Guardian says section 5 of the 1989 Official Secrets Act allows prosecutions for passing on "damaging" information leaked to them by government officials in breach of section 4 of the same act, including police information "likely to impede … the prosecution of suspected offenders".
According to the paper, there has been only one previous attempt to use the act against a journalist, in a case which collapsed in 2000.
A BBC correspondent said it's highly unusual for the Official Secrets Act to be used in this way; the act prohibits the disclosure of material that may impede the detection of crime.
The BBC reports 16 people have been arrested on suspicion of phone hacking since January.
The scandal led Police Commissioner Sir Paul Stephenson and Assistant Commissioner John Yates to resign and the News of the World to close after 168 years.
In a statement, the Met Police said:
''We pay tribute to the Guardian's unwavering determination to expose the hacking scandal and their challenge around the initial police response.
''We also recognise the important public interest of whistle blowing and investigative reporting, however neither is apparent in this case.''