They aren't paid hourly, and the employee signs the contract saying they are okay with not being able to do thing on the side without approval.

It might not be enforceable but it would take a very brave or wealthy individual to choose to do something that might make Amazon decide to sick their lawyers on you.

Months in court to prove innocence is still a heavy cost to pay.

If the mass can side with you, you can fight with donations to represent them all.

Not that I agree with Amazon's policy for no open source contributions, but imagine that an employee decides to spend the 6-8hrs out of the remaining 24hrs meant for sleep on something other than sleep, what do you think will happen? That employee's productivity during those critical 8hrs of the day that is being paid for by the employer would drop like a rock, because whether we like it or not, we need time to recharge our batteries.

That's... wow. Are you saying that the employers could (or even should) demand that employees do nothing else during their free time except rest, so that they are well rested for their on-the-clock time? No late night TV for you, no early morning pool swimming session, and don't even think about taking up that physically demanding hobby, because we need you 100% focused on the job!

No. I specifically said remaining hours.

To recap:

   - 8hrs for work;
   - 8hrs for leisure (daily commute, family time, hobbies etc);
   - 8hrs for sleep.

Once you take out work time & leisure time all you have left is sleep time. Sleep is unique because it is an exclusive human activity — it can’t be combined with other activities.

If someone decides to misallocate rest time, then s/he will become sleep deprived leading to low productivity. This is true regardless of whether you perform physically demanding work like farming or sit all day at a desk doing knowledge work.

A self-inflicted impairment like this is no different from abusing hard drugs or consuming too much alcohol (on or off the clock), but it is vastly different from low productivity resulting from falling ill, which is beyond any employee’s control.

Whether you like it or not, paid employment demands a certain monopoly of your time. The only way to opt out is to work for yourself.

In my view, contribution to open source falls under hobbies, so the time comes from the leisure time.

I agree that if someone takes that from sleep time instead, they're harming themselves, but this still is nothing the employer should (be allowed to) care about.

If the employee underperforms at work, the employee gets a warning, and it is up to the employee to review his or her time management, being a responsible adult that they are.

I think what the post above yours is trying to say is that the company I work for has no say what I do with my 8 hours of sleep time. If I want to only sleep for 4 hours but I come to work and get my job done, who cares? It is my time anyway and they aren't paying me to sleep so why should they have a say? If my work is suffering, sure, they have a right to fire me but if I get my work done in the 8 hours, they have no say over the other 16.

If someone is badly underperforming, then they can fire them. It's simply ridiculous for a company to own a second of your time outside work hours, excepting things like people on call, of course, but I count that under work hours.

By that argument they should also prohibit people from playing competitive chess outside of work, because it's mentally challenging.