Final answer:
Contractual or consumer protection laws require Dr. Giles to notify patients of changes in policy regarding charging interest on unpaid balances, ensuring transparency and informed decisions.
Step-by-step explanation:
The law that requires Dr. Giles and his practice manager to notify patients about the change in policy regarding charging interest on unpaid balances likely falls under contractual or consumer protection laws. When altering the terms of an agreement with patients, especially concerning financial matters like interest charges, it is generally required by law to provide clear and timely communication of these changes. This ensures transparency and allows patients to make informed decisions regarding their continued use of the services provided by Dr. Giles's practice.