By default, your MobileCause forms will accept any major credit card. But there are cases where you may have an exclusive deal with one, such as Visa, or you may not want to accept a specific type, like Diner's or Amex. In these cases you would want to limit the types of credit cards you will accept.
Go to Settings > Payment Methods.
Once in Payment Methods, you will now be able to select/deselect which credit card types you wish to receive, and then click Save.
If you deselect one or more of the major four credit card types (Visa, Mastercard, American Express, Discover), the icons for those credit cards will disappear from your form.