Could be a silly question. I do know many software companies that prevent / have a write up on how the clients cannot use a competitor product for a specific time/ duration after they stop using their services. Do companies like Mastercard and Visa have something similar that a client cannot use mastercard if they prefer VISA as their primary vendor? I do hear at some places that they do not accept master card / AMEX, is this a competitor aggrement that stops them from using master card / AMEX (or) is it the high processing fee that stops them from using their services?
In short: Is there any way a client using VISA be restricted from using mastercard's service (or) vice versa?