20 plus years working for national food service provider hired to work 5days a week told as of December 16 work week will be four day rotating max 8hrday does this fall under constructive dismissal or wrongful dismissal or maybe both approx 18 thousand year drop in salary thank you

It certainly sounds like it, although if you were advised of this back in December and worked the new schedule since then, the company might be able to argue that you acquiesced to the changes. Time is of the essence here, and so I strongly recommend that you seek immediate legal advice at the number below.