He’s not the only one who can’t make it.

If your company pays employees hourly, it’s a lot harder to get away with not paying overtime. If they have to clock X hours and their work requires them to work more than X hours, it’s obviously unethical not to pay them for that time. In fact, you might even have to pay your employees more for making them work overtime. 

If you’re working in a salaried position, it’s much more difficult to get them to pay for overtime. A great deal of the time, there is nothing in your employment contract that denotes that you’re entitled to overtime pay. You could negotiate for it, but that will be much more difficult the more money you make. If you’re earning a high salary, your boss might assume overtime pay isn’t necessary. 

The best thing employers can do is be honest about their expectations during interviews. They should tell them they expect them to come in at least once a month on weekends. The prospective employee might not like that, but at least they know what they’re getting into if they decide to take the job offer. If a company springs weekend work on its employees out of nowhere, the employees have the right to be angry and to fight back. They may not win, but they shouldn’t be expected to attend mandatory weekend work functions when that obligation is nowhere written in their employment contract.