Contractor agreements are like agency agreements. The contract employee is a party to the agreement.
This is like colluding to set the price of LCD displays or chips. That's illegal. Even an HR director should know that.
This is like colluding to set the price of LCD displays or chips. That's illegal. Even an HR director should know that.
Even if you somehow forced everyone to be part of the agreement, it's irrelevant - whether Apple's and Google's employment contracts had language that forced the employees to agree to what's going on here is not exactly relevant consideration.
Edit: part of the irony of this whole "non-solicitation agreements are illegal" chorus is that I think most people complaining probably have signed such agreements in the past as they are quite routine. Granted, most of the time, it's just handed to us and we have to sign or gtfo.