The Magnuson-Moss Warranty Act, which some exceptions, prohibits including a “tie-in sales” provision in a warranty. Generally, it is illegal for manufacturers or dealers to claim that a warranty is void or to deny coverage under a warranty simply because someone other than a specific company did the work. The manufacturer or dealer can, however, require consumers to use select repair facilities if the repair services are provided to consumers free of charge under the warranty. Read more at link below: