What is it called when you pay a fee for service?

What is it called when you pay a fee for service?
It's called fee-for-service. At our agency we have some full-time employees, some part-time employees, some volunteers and we have some fee-for-service counselors. They are paid for the services they provide and no more. The amount they are paid every 2 weeks depends completely on the number of service units they have provided. Part-time employees are paid a regular amount based on contract; this is different from fee-for-service. If you are thinking about signs that you sometimes see, "Fee is due at time of service" this simply means that you have to provide proof of some kind of coverage at the time of service, or be prepared to pay in cash at the time service is provided.