Visa has elected to enable merchants to elect to accept Visa debit separate from credit. It's commonly referred to as the honour-all-cards rule that Visa has, and they do have that rule. So if you accept a Visa credit card, you have to accept all Visa credit cards. But they've made the choice to say that if you don't want to accept Visa debit and you just want to stay with Interac, that's okay. That's allowed.
On May 26th, 2009. See this statement in context.