No. As long as they don't expect to clock an exact 40 every week. If we just finished a sprint and things are going well, I'm happy to tell people to go home or take a break.
If we're in a sprint, or shit hits the fan, or revenue is down, or anything else that requires hands on deck, I expect people to complete the task, even if it means more than 40 hours.
There are plenty of businesses making things that, if they stopped making them, would not stop the world from turning. The point is, it's a business, who is likely competing against many other businesses that would be all-to-happy to scoop up their market share. I don't agree that employees should be expected to consistently work more than 40 hours week after week. I do agree that when situations arise in business that requires full and focused effort of entire departments or the whole company, the managers/owners first better come to the employees, with hat-in-hand, and discuss why this is important for the company and the team before issuing their mandatory overtime decree.
I assume that your employees have worked at least one week with over 60 hours. Would you accept them working only 20 hours another week? Why should employees donate extra time to a for profit project if you can't do the same.
If a situation arise because of bad planning an employe are expected to donate their time, but if an employee finish the sprint early the company will find something extra for them to do.