Ontario unpaid invoice: is there a deadline to sue?

Ontario’s Limitations Act has a basic limitation period of 2 years from the day a claim is discovered, unless an exception applies. For an unpaid invoice, the exact start date can depend on the contract and when payment became due, so businesses should not leave recovery until the last minute. Official source: Ontario Limitations Act. Guide: https://getinstantlaw.com/small-business/customer-wont-pay-invoice