Convenience fees are often applied to credit card transactions by businesses when it is considered to be an alternate form of payment that falls outside their normal business practices.
A few opinions on this practice:
1). Many of these fees are excessive (my utility company charges a $7.50 convenience fee for what is typically a ~$45 utility bill).
2). It discourages consumers from transitioning towards paperless billing, which impacts the environment.
2). For many merchants, this is seemingly unjustified. Electronic payment is convenient for both consumers and providers of services and goods. Depending on average transaction size, allowing credit/debit cards as a form of payment can actually save merchants money in the long run.