As you may have read on the front page [https://www.macrumors.com/2016/02/05/error-53-home-button-iphone-brick/], Apple is bricking iPhone that have had Touch ID repaired with 'Error 53'.
This violate the law, specifically the Magnuson-Moss Warranty Act of 1975.
The law was specifically passed because in the past, car manufacturers were voiding the warranty for those who took their car to independent mechanics for repair.
Source: http://www.consumer.ftc.gov/articles/0138-auto-warranties-routine-maintenance
This law is however, not limited to automobiles and, but applies to consumer products such as the iPhone.
By bricking the iPhones, Apple has gone beyond no only voiding the warranty, but also render the products unusable.
This violate the law, specifically the Magnuson-Moss Warranty Act of 1975.
The law was specifically passed because in the past, car manufacturers were voiding the warranty for those who took their car to independent mechanics for repair.
Do I have to use the dealer for repairs and maintenance to keep my warranty in effect?
No. An independent mechanic, a retail chain shop, or even you yourself can do routine maintenance and repairs on your vehicle. In fact, the Magnuson-Moss Warranty Act, which is enforced by the FTC, makes it illegal for manufacturers or dealers to claim that your warranty is void or to deny coverage under your warranty simply because someone other than the dealer 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.
That said, there may be certain situations where a repair may not be covered. For example, if you or your mechanic replaced a belt improperly and your engine is damaged as a result, your manufacturer or dealer may deny responsibility for fixing the engine under the warranty. However, according to the FTC, the manufacturer or dealer must be able to demonstrate that it was the improper belt replacement — rather than some other defect — that caused the damage to your engine. The warranty would still be in effect for other parts of your car.
Will using 'aftermarket' or recycled parts void my warranty?
No. An 'aftermarket' part is a part made by a company other than the vehicle manufacturer or the original equipment manufacturer. A 'recycled' part is a part that was made for and installed in a new vehicle by the manufacturer or the original equipment manufacturer, and later removed from the vehicle and made available for resale or reuse. Simply using an aftermarket or recycled part does not void your warranty. The Magnuson-Moss Warranty Act makes it illegal for companies to void your warranty or deny coverage under the warranty simply because you used an aftermarket or recycled part. The manufacturer or dealer can, however, require consumers to use select parts if those parts are provided to consumers free of charge under the warranty.
Still, if it turns out that the aftermarket or recycled part was itself defective or wasn't installed correctly, and it causes damage to another part that is covered under the warranty, the manufacturer or dealer has the right to deny coverage for that part and charge you for any repairs. The FTC says the manufacturer or dealer must show that the aftermarket or recycled part caused the need for repairs before denying warranty coverage.
Source: http://www.consumer.ftc.gov/articles/0138-auto-warranties-routine-maintenance
This law is however, not limited to automobiles and, but applies to consumer products such as the iPhone.
By bricking the iPhones, Apple has gone beyond no only voiding the warranty, but also render the products unusable.