Letters are to be sent "imminently" to those likely to be criticised in a report into the death of Jean Charles de Menezes, the police watchdog says.
Jean Charles de Menezes was shot dead at Stockwell Tube station
The formal warning letters will be sent as part of the Independent Police Complaints Commission (IPCC) inquiry into the Stockwell Tube shooting.
Mr Menezes was shot seven times in the head by firearms officers in a London Tube carriage in July 2005.
The IPCC launched an investigation and is due to publish its report in March.
Officials said the warning "Salmon letters" will be sent to all those who may face criticism as a result of the inquiry into the shooting on the London Underground on 22 July 2005.
A spokeswoman for the IPCC would not confirm to whom the letters would be sent.
"We are about to commence sending out Salmon letters imminently - today or tomorrow," she said.
"The Salmon letters are due to go out to a number of individuals, we are not commenting on any speculation."
The Salmon letter is named after Lord Justice Salmon, who chaired a royal commission into public inquiries in 1966.
He recommended that warnings and details of accusations should be sent to anyone who might face criticism.
Last month the IPCC said no-one should "make any assumptions" about the report's conclusions.
After the letters have been sent, the recipients will be given the chance to respond.
The report will then be given to the Metropolitan Police Authority before it is published.
Mr Menezes, 27, a Brazilian electrician, was shot inside a train at Stockwell Tube station in south London by police who mistook him for a suicide bomber.
It was a day after an alleged attempt to detonate bombs on London's transport network and two weeks after the 7 July terror attacks.
The IPCC's inquiry, which was launched a month after the shooting and is codenamed "Stockwell 2", investigated complaints by the family of Mr de Menezes over police statements about the shooting.