The Australian Federal Police says it "made a mistake" in accessing a journalist's metadata without proper prior approvals.
The breach occurred earlier this year in the AFP's internal investigations unit where an investigator gained access to the journalist's phone records without the prior authority of a Journalist Information Warrant.
AFP Commissioner Andrew Colvin said the agency took full responsibility for breaching the Telecommunications (Interception and Access) Act.
But he stressed there was no ill-will nor malice by the investigators who made "a mistake".
"This was human error; it should not have occurred," he told reporters in Canberra.
"The AFP takes it very seriously."
The AFP was investigating the unauthorised release of sensitive police information to a journalist, Mr Colvin said.
The journalist has yet to be informed of the breach as investigations are still ongoing.
The records were in relation to one phone number calling another, and the time, date and duration of the call.
The content of the call was not breached.
This was the first investigation where the AFP was required to obtain a Journalist Information Warrant under the Act.
The Commonwealth Ombudsman will launch an audit of the breach on May 5.
