Employee is hired and signs a fairly standard compensation agreement.

Several months into employment the same compensation agreement is re-issued except this time it now has an amendment.

The amendment was a paragraph mentioning that if the employee voluntarily left prior to a certain date that all guaranteed bonus/commission money would have to be paid back.

Are these iron clad deals with no room for debate/argument? Or does the employee have a case because the “payback” part of the agreement was introduced well into employment where the employee was forced to either sign it or else be let go?

Almost feels like corporate extortion.