What is a credit card surcharge?
Surcharge is the additional fee added to a credit card transaction, so everything you buy using credit cards could potentially cost more.
Why do merchant stores require a surcharge?
For every successful card payment, the merchant has to pay a service fee to the bank or payment gateway. Instead of absorbing the cost, they can migrate the cost to the end user. Generally, cash payment transactions are free of surcharge.
A business should consider the following questions:
1. What will my customer think?
Not all customers are willing to pay an additional fee. Surcharge can put off a customer that is already giving you business.
2. Do I need to tell my customer?
Some merchants add the fee directly.
3. Does my competitor do it?
Your product or service will be slightly more expensive than that of a competitor. Surcharge may affect the volume of sales.
4. Is surcharging permitted in my state?
The rules vary for every country. In the US, some states do not allow surchage.
5. How much can I charge?
The cost must be lower than credit card processing fees. Under no circumstances can the merchant assess a surcharge of above 4%.

Source: usa.visa.com