Can an Ontario employer require employees to be on call without paying them for that time?

It depends on what being "on call" actually requires of the employee, which is the detail that gets missed most often. Under the Employment Standards Act, 2000, time genuinely counts as hours of work, and generally needs to be paid, where the employee is required to remain at the workplace or is otherwise not free to use the time for their own purposes while waiting to be called in. Simply being reachable by phone from home, free to go about ordinary activities, and only occasionally called in to actually work, is treated differently from being required to stay at or near the workplace on standby.

Where an employee is called in to actually perform work while on call, that time worked generally counts as hours of work and needs to be paid, including at overtime rates if it pushes total weekly hours past the threshold. The unpaid gap employers sometimes assume exists for "waiting to be called" doesn't automatically extend to time when the employee is meaningfully restricted in how they can use it.

Because the on-call pay line depends heavily on the actual restrictions placed on the employee, not just the label "on call," employers should look closely at the real conditions before assuming no pay is owed.