Amy, that sounds very reasonable, providing it is a genuine consultation period. To get "buy in" you could also point out that you are formalising a benefit scheme which is currently discretionary (assuming that is what your intention is!). This in itself will give the staff more security in terms of their remuneration.
Just make sure the new scheme is fair and that they will have the same opportunity to earn commission and at the same levels. It would also be a good if you can anticipate any obvious resistance or objections.
Of course this is just my personal opinion - the usual disclaimers apply