Ads are typically bought and sold through automated auctions and managed by businesses using ad tech -- a system that also decides which online advertisements people see when they visit websites.

A Competition Bureau investigation found that Google is the largest provider of these tools in Canada.

Commissioner Matthew Boswell said in a statement it "has abused its dominant position... by engaging in conduct that locks market participants into using its own ad tech tools."

The watchdog accused Google of giving its own tools preferential access to ad inventory, at times selling ads at a loss to block rivals, and dictating terms for the use of others' ad tech tools.

Boswell said he would ask a tribunal to level the playing field by forcing Google to sell two of its ad tech tools and pay an unspecified penalty.

Google spokesman Dan Taylor said the company is prepared to fight the allegations that he said "ignore the intense competition (in this sector) where ad buyers and sellers have plenty of choice."

France's competition watchdog fined Google 220 million euros in June 2021 for favoring its own services in the online advertising sector.

Google's advertising practices are also subject to investigations or proceedings in Britain, the EU and the United States.

The technology giant and the US government faced off in a federal court this week in a case revolving around Google's alleged unfair domination of online advertising.

If the judge finds Google to be at fault, a new phase of the trial would decide how the company should comply with that conclusion.