[Tenhundfeld]

No, continued employment is not incentive, not under the law explained to me when I lived in AL.

Anyway, it varies by state and the exact situation. It's not necessarily true for any change, only if it withdraws a substantial right, e.g., forces arbitration or changes the nature of IP ownership. If you are concerned, talk to a local lawyer.

My real point was that it's not necessarily true that you just are automatically bound by the updated contract or that you have to sign it. It might be true, might not.