This isn't an airline charge, but it is charged by rental car companies located within airports. These businesses have to pay fees to the airport to operate in their facilities, and they pass the charges on to you in the form of a concession recovery fee.
This charge can increase the cost of the car rental by up to 20 percent. To avoid paying extra, consider renting a car at a nonairport location. Just make sure the company offers a lower rate at the other location and doesn't inflate the price to match what's charged at the airport facility.