Probably not, but there are a bunch of variables at work here.
First question: Do you have a preexisting written agreement with the sales people? If so, are the commission changes less favorable than the original terms? If the answer to both of those questions is yes, the changes won’t be enforceable even if employees do sign UNLESS you give them what’s called consideration, or something of value in exchange for accepting the new terms. Consideration must be something the employees didn’t have before. So, if like many employers do, you make “employment” or “continued employment” the consideration, it won’t work–although that probably will work for new employees you don’t already employ.
The wildcard in all of this is what the original contract says or doesn’t say. Specifically, is there anything in the agreement that gives you the right to modify the commission terms unilaterally? If so, you should be on solid ground.
Bottom Line: Try to get everybody to sign and make sure you’re giving them consideration, unless the contract says you can make unilateral changes, in which case you don’t have to deal with the consideration problem. Hope that helps.
