You need to remember that this is a "value for value exchange" - and they are giving you less. They have changed your contract unilaterally. You are entitled to come back at them and renegotiate the contract. (It probably won't do any good, but I would try.)

"Hey, I see you've reduced my compensation. Let's discuss my new salary."

As for behavior; are you a professional? A professional performs to best of their ability. Take a fireman or a teacher; they don't "Do the bare minimum expected of you".

I would just leave.