Can a business sue a customer for defamation over a negative online review in Ontario?

Yes, in principle. A business can pursue a defamation claim over a negative online review if the review contains false statements of fact that damage its reputation, rather than a genuine expression of the reviewer's personal opinion or experience. This is where these claims often become difficult in practice: an honestly held opinion about bad service, or a truthful account of what actually happened during a transaction, is generally protected and will not support a defamation claim, even if it is harsh or damaging to the business involved.

The claim usually needs to focus on specific, false factual assertions within the review - claiming something happened that did not, or attributing conduct to the business that is simply untrue - rather than the reviewer's overall negative impression of the experience. Because these cases risk looking like an attempt to silence legitimate customer criticism, and because both truth and fair comment are available defences to a reviewer, businesses considering this route should carefully assess whether the review actually crosses from opinion into false factual claims before pursuing legal action over it.