if they are making them sign something "under duress" than most any good attorney could get that overturned in court.
However, the questions of is the avererage GC employee about to procure a good attorney, and would the legal fees be almost as much as thier annual salary...and exactly what are you fighting for if the company is so close to shuting it's doors anyway...are more pertinent than the initial legality question in the first place. they are basically saying "quit now and go to sam ash before you are competing with the rest of all GC employees in getting those jobs," so in a way with writing on the wall, this is better than a mass layoff without warning. you sign the document, keep your currennt employment, and for any one of many, many reasons...start job hunting!