Need to talk to a lawyer to have him review the agreement.
Most of the time if you are a white man your recourses are nil, you just have to move on.
Two possibilities are Age Discrimination or Detrimental Reliance, if neither of these apply to you, more than likely regardless of the cause they can fire you.
So don’t get your hopes up, most states are employment at will. Meaning that if there is no contract, either party can quit the relationship for any reason.
If Wisconsin is one of these states, they are likely just being nice and hedging their bets to make sure that you don’t come back and tie them in knots in court.
Waste of money. The agreement is a simple one page document. Folks here are making too much out of a common every day occurance..... Over 30 years in HR, both plant side and corporate and received the same letter in my 34th year.
Just move on....