George Michael's family have said they are "appalled" a 999 call made about the singer on the day he died was apparently leaked to the press.
In a statement from their solicitors, the family called for the "culprit(s) to be dealt with appropriately".
South Central Ambulance Service said an investigation had been launched.
The former Wham! frontman was found dead on Christmas Day at his home in Goring-on-Thames, Oxfordshire.
'Deeply distressing'
A statement from the family's lawyers said: "George's family and friends are extremely upset and truly appalled that such a personal, painful and clearly confidential recording has been leaked.
"We firmly believe that anyone contacting the emergency authorities in situations such as this should be entitled to expect that recordings will not be released to the media and it is deeply distressing to the family that this transcript, and audio recording, has been made public."
A spokeswoman for South Central Ambulance Service said: "We take matters of confidentiality very seriously and have launched an immediate investigation."
A post-mortem examination was inconclusive and more tests are being carried out.