https://www.ftc.gov/tips-advice/busi...l-warranty-law
"Tie-In Sales" Provisions
Generally, tie-in sales provisions aren’t allowed. That’s a provision that requires a consumer to buy an item or service from a particular company to keep their warranty coverage. Here is an example of prohibited tie-in sales provisions.
To keep your new Plenum Brand Vacuum Cleaner warranty in effect, you must use genuine Plenum Brand Filter Bags. Failure to have scheduled maintenance performed, at your expense, by the Great American Maintenance Company, Inc., voids this warranty.
However, a warrantor can require a consumer to use select items or service if they’re provided free of charge under the warranty.