Comment by Hannan

It's complicated and depends on things like where you're charging and whether or not it's a "fee" for using the card vs. offering a cash discount (how these are not essentially equivalent is beyond me):

Sections 1.5.4.2 & 5.6

https://usa.visa.com/dam/VCOM/download/about-visa/15-April-2...

Section 5.11.2

https://www.mastercard.us/content/dam/mccom/en-us/documents/...

IANAL, etc.