Mike McCormack, the president of the Toronto Police Association, told CBC News on Tuesday that he couldn't talk about the details of the incident, though the officers "were responding to somebody who was armed with a firearm."
The province's Special Investigations Unit is probing the shooting.
The man remains in hospital in serious condition, but is expected to survive.
The SIU has said a total of nine officers responded to reports of a "suspicious person" on a subway train. Four officers are believed to have fired their guns, according to the SIU.
The man, whose name has not been released, was shot a number of times and remains in hospital.
The SIU is called in whenever police officers are involved in incidents in which someone has been seriously injured, killed or has alleged sexual assault.