Are companies required to pay wages for travel time outside of regular hours?

My company routinely signs me up for conferences and meetings that are often 3-4hrs away from where I live. Typically these meetings run past our office hours. So given that I work till 4pm and a meeting may end at 4-5pm or later, if I have to drive home from that meeting which can take up to 4hrs sometimes, is that not considered work? I mean I'm not traveling for my own leisure but for business purposes and so if I have to drive 4hrs and its not within my paid hour time should this not be considered work related activity and thus be considered payable hours? I work in Ontario and I cant seem to find any info on it on the web. I've asked my employer about this and they pretty much tell me tough luck. I didn't sign a contract with the stipulation that I wouldn't be paid for this type of thing so I didn't exactly agree to it. I wouldn't make a fuss if they would just pay for a hotel sometimes but they seem to expect me to drive home no matter how late a meeting/conference ends and I get no compensation for that time and that just seems really unfair to me?