This is part of the Magnuson Moss Warranty Act: https://en.wikipedia.org/wiki/Magnuson%E2%80%93Moss_Warranty...
In effect, the manufacturer can only deny warranty claims for a specific part iff the consumer's aftermarket repair/modifications were responsible for the warrantied part failing. i.e. "I tinted the windows, and now the brakes are failing" does not result in warranty claims on the brakes being denied. However, "I replaced the brake pads [with faulty pads], and now the brake rotors are failing" can result in a denied warranty claim.