No, we are not really talking about unvested shares to be earned in the future. We're talking about unvested shares. These are shares that employees have already been paid. This payment is contingent upon the employee continuing to work at the company. Zynga is in effect blackmailing these employees. They are telling them "Give us this money we promised you, or we'll fire you."

The idea behind putting together a plan to keep early employees highly motivated is that you all work hard to grow the company, and in return for the risk and hard work you stand to make a lot of money. That's the whole idea behind tech startups. To grow the company and then tell these employees they don't get the rewards promised them the entire time they have worked there is ridiculous. It violates the entire idea behind vesting shares, which if it is unclear, is that you have already earned those shares. It's merely a matter of when you gain access to them.