Ainslie called an impromptu news conference Thursday to inform reporters that he was stopped by police on or about May 3 at a RIDE checkpoint.
The councilor for Scarborough East said he had consumed "a couple of" glasses of wine that evening.
A subsequent roadside test determined that his blood-alcohol level in the warn range of between .05 and .08.
Ainslie said he was issued the warning along with a three-day licence suspension but was not charged.
"This incident serves as a stark reminder to me of the dangers of consuming alcohol prior to driving," Ainslie said.
Blood-alcohol content is a measure of the amount of alcohol present in a 100 milliliters of blood.
Police issue roadside suspensions when a driver's blood-alcohol content falls between .05 and .08 . A first-time offence results in a warning and a $150 fine.