I am not suggesting that if you drop a chocolate bar on the ground, it's fine to eat it as long as you pick it up within three hours. That's nasty.
I'm talking about one of those myths about the ESA (the Employment Standards Act - the labour law in the province of Ontario). There's a notion out there among hourly workers that if you come in to work, you have to get paid for three hours no matter how short the duration of your shift happens to be. This is wrong - or at least not quite right.
First, you can be scheduled for a shift less than three hours. If they book you to work from noon to one, you get one hour's pay. That's it. (By the way, if your boss does that without a good reason, s/he probably wants you to quit - it's probably constructive dismissal, a topic for another post.)
But now to the real crux of this myth: if you are scheduled for a shift longer than three hours, and they send you home before three hours, you are not necessarily entitled to three hours pay. The ESA states that you are entitled to the amount you earned at your hourly rate for the time you were on duty or three hours pay at minimum wage.
I can't remember what minimum wage is right now (it's been changing a lot in the past few years), but let's say that it's $10. So what if you get sent home after 2 hours? Let's look at two scenarios:
1. You make $12/hour
In this situation, 2 hours work at $12/hour gives you $24.
3 hours work at minimum wage gives you $30.
So, your boss has to pay you $30.
(If s/he's on the ball, you'll wind up working an extra half hour doing some boring task so that they get the full $30 worth of work out of you.)
2. You make $16/hour
Now, after 2 hours, you have earned $32.
Since 3 hours at minimum wage is $30, your boss has to pay you $32.
This is quite progressive legislation. The lower your wage, the more likely you are to benefit. Depending on your outlook, this will either be a way of protecting the little guy, or a situation where a bunch of people get screwed - but if this happens to you a lot, it is a blessing in disguise, as it will give you a lot of extra time to search for a new job because the current one just ain't gonna cut it.