There is absolutely no reason why you can not have your vehicle routinely serviced outside of the dealership because of warranty obligations! You most certainly have a right!
The Magnuson-Moss Warranty Act (15 U.S.C. 2302(C))
This federal law regulates warranties for the protection of consumers. The essence of the law concerning aftermarket auto parts is that a vehicle manufacturer may not condition a written or implied warranty on the consumers using parts or services which are identified by brand, trade, or corporate name unless the parts or service are provided free of charge. The law means that the use of an aftermarket part alone is not cause for denying the warranty. However, the law’s protection does not extend to aftermarket parts in situations where such parts actually caused the damage being claimed under the warranty. The law states in relevant part: No warrantor of a consumer product may condition his written or implied warranty of such product on the consumers using, in connection with such product, any article or service (other than article or service provided without charge under the terms of the warranty) which is identified by brand, trade or corporate name… (15 U.S.C. 2302(C)).