Fom the Pros at the HR Support Center
The Department of Labor considers any break under 20 minutes to be for the benefit of the employer, and therefore those breaks must be paid. However, unauthorized extensions of authorized breaks do not need to be counted as hours worked if the employer has expressly and unambiguously communicated to employees that authorized breaks may only last for a specific length of time, that any extension of the break is contrary to the employer’s rules, and any extension of the break will be punished.
Your recourse when employees take unauthorized breaks under 20 minutes is discipline, not reduction of pay. Employees who take longer breaks than authorized can have their pay reduced for the extra time, but discipline is still a good idea to prevent it from becoming a habit that ultimately cuts into productivity.