Section 700.10 of the Federal Trade Commission Interpretation of the Magnuson Moss Warranty Act (16 C.F.R. Part 700):
No warrantor may condition the continued validity of a warranty on the use of only authorized repair service and/or authorized replacement parts for non-warranty service and maintenance.
For example, provisions such as, "This warranty is void if service is performed by anyone other than an authorized 'ABC' dealer and all replacement parts must be genuine 'ABC' parts," and the like, are prohibited where the service or parts are not covered by the warranty. These provisions violate the Act in two ways. First, they violate the section 102(c) ban against tying arrangements. Second, such provisions are deceptive under section 110 of the Act, because
a warrantor cannot, as a matter of law, avoid liability under a written warranty where a defect is unrelated to the use by a consumer of "unauthorized" articles or service. This does not preclude a warrantor from expressly excluding liability for defects or damage caused by such "unauthorized" articles or service;
nor does it preclude the warrantor from denying liability where the warrantor can demonstrate that the defect or damage was so caused.
source: http://law.justia.com/us/cfr/title16/16-1.0.1.7.71.0.45.10.html
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