In its services and repair terms and conditions, Google says it will keep devices sent in for repair if they have a non-OEM part.
Update:
Google changes repair policy after criticism of third-party parts ban Google previously said it would not return mailed-in devices using “unauthorized” parts.
Depends. Where I live even signed contracts can be deemed illegal in parts if a clause is still seen as unexpected or surprising for the customer.
If Google included a clause that states the customer loses a kidney to them, wouldn’t make it legal just because it’s written there.
It’s legal in the United States where consumer protection laws aren’t as strong as in some other places.