What is the law that mandates taking a 15 minute break at work?

The Fair Labor Standards Act does not require employers to offer any type of meal or rest breaks. As of 2015, 22 states have laws requiring some type of break, but only seven of those states require both types of breaks. All of the state laws vary in break length.

If employers choose to offer rest breaks between five and 20 minutes long, the federal government considers them compensatory and included in the paid week hours. If a break is for 30 minutes or more, then no compensation is required. Checking the labor laws for a specific state is the best way to learn what the prevailing law is in a given area.