Emails have been going around, claiming that Battle.net Accounts are breaking the ToS—varying from selling your account, modding your games, etc.
These are the work of phishing attempts trying to get your password, having hacked Blizzard to get your email, then sending a bogus alert and sending you to a fake log-in screen.
Do NOT click the links on these emails, log in to the Battle.net App or the site itself and check your account. If there’s no alert from Blizzard, you’re being tricked. Blizzard NEVER asks for passwords.