If you are caught letting or making your employees work beyond the set work hours, which would be 40 regular hours per week plus 8 hours overtime per week (can be 5 days at 8 hours or 4 days at 10 hours), the fine for a company is pretty hefty. (Except Engineers and seasonal labour, and farm workers, medical, emergencies etc. and by engineer I mean professional engineers who have passed the engineer society test and wear the engineer ring. No just being called a software engineer does not make you an Engineer. Are you a me,ber of the society of professional engineers? Not, not an engineer.)
That is the law in Canada for federally regulated industries so if your employer says you have to work but you have already done 48 hours remind them of the labour code. (Anything over 40 per week must be at least time and a half, by law. "free time" donated or volunteered is just illegal, the labour code stipulates that time worked is time paid and that all overtime, that is time spent doing any work beyond 40 a week must be paid at at least time and a half. I doubt your boss wants to pay fines of 10 times that instead of paying the overtime. And there are jail terms for real bad bosses or trying to cover up the over time, it just gets to be fraud at that point and if they know this they won't allow you to do unpaid work.)
Federal holidays worked are overtime, any call in (or if you are paged for something to fix remotely) is an automatic pay of 4 hours even if it just takes a minute and it counts against your total for the week. So call me after I already worked a full day and ask me to reset the server is overtime for 4 hours and do it 2 days in a row and you may as well let me have Friday off because it's suddenly overtime.
If you have booked paid vacation and you get a call in or pager or whatever it is automatically 4 hours of overtime. Also You have to have 1 24 hour period where you do not book any hours or do any work for your employer; by law. taking something home to work on counts as work done even if you don't get paid, it is legally hours worked and if it takes you beyond 48 for the week then your employer could be held liable and fined. if you are in a shop where someone might resent you doing the "free" work and are preasured to do the same as you could report you and the employer and then it just gets bad all around. Your employer should be telling you not to work the free hours because the fines are more than the time spent is worth. They should just hire more staff it is cheaper than the fines.
Consultants and self employed also have limits but they are higher and who is going to report you, yourself? Well how about disgruntled employees, ex employees and competitors. (or your wife if she gets vindictive and wants to really mess you up.)
It is in your employers best interests to pay you for hours worked and properly account for those hours. Not doing it and telling you to work for free or not charge hours worked or coverup hours worked past the weekly limits is not in their interest and if they still insist on it report them, reports can be anonymous, and we have whistle blowing laws so employers can not afford to try to go beyond the law. (Applies if you are union or not, full time or part time, temp or perm staff. get to know the labour laws in your country, In Canada go to the federal government web site http://www.hrsdc.gc.ca/eng/labour/overviews/employment_standards/hours.shtml
Hope this helps.