Motability has sent a leaflet to 500,000 people with disabilities who are eligible to benefit from its contract hire car scheme.
The charity is concerned that although an estimated 1.6 million people with disabilities qualify for the scheme, only 400,000 currently take advantage of it.
The leaflet says that all those who receive the higher rate disability living allowance qualify for a new car, powered wheelchair or scooter.
Benefits of the scheme include a new car every three years and a mileage allowance of 45,000 miles for that period.
Don Brereton, director of Motability, hailed the campaign as an "excellent first step towards ensuring that everyone who is eligible for transport through us is made aware of the fact."