Can't find source but I remember reading here the story of a payment business that competed with VISA and was taking off until VISA started threatening his client, making them fear that their payment wouldn't be processed at some point, and they would be subject to fines, if not worse.

I remember reading other stories on the same line, about visa using shady approaches to frighten people to preserve their monopoly, but a quick search can't bring any up. Search terms are too generic.