The notice by the Law Society of Upper Canada warns that a lawyer who acts for multiple officers could end up in an untenable position of conflict.
"This notice by the Law Society will do much to advance the cause of civilian oversight of law enforcement," said Ian Scott, director of Ontario's Special Investigations Unit.
"It is now clear that a lawyer cannot act for more than one police officer in relation to SIU investigations."
Normally, a lawyer acting for several clients in a case is required under professional rules to disclose information obtained by one to the others.
The issue has been a sore point for the Special Investigations Unit — a civilian watchdog — and has been the subject of ongoing litigation by two families with relatives killed by police.
The families argued that sharing a lawyer allowed collusion among officers under investigation in violation of rules that officers involved in an incident not communicate with one another.
The law society notice, issued November 6, points out that Ontario's regulations prohibit officers under investigation for causing death or serious injury from being represented by the same legal counsel as witness officers.
The rules call for the chief of police to "segregate all police officers" involved in the incident from one another until after the special investigations unit has completed its interviews.
In the past, officers have routinely retained the same lawyer. Their association has argued it's the same right to choose counsel that other citizens enjoy.
The law society argues the situation is different when it comes to acting for police.
"A lawyer retained to act for multiple officers must observe the law and not defeat the purpose of (the rules) by serving as a conduit between segregated officers," the law society said.
"Further, the law requires that a lawyer retained to act for multiple officers must not disclose anything, confidential or otherwise, said by one segregated officer to any other segregated officer until the SIU has completed its interviews."
Given the various directives and rules, the law society said it was difficult to see how segregated police officers can properly be jointly represented.
The notice also urged lawyers to review a year-old decision in which Ontario's top court ruled that officers under investigation by the civilian watchdog had no right to legal help in preparing their notes.
The Special Investigations Unit is an arm’s length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.