Answered by the HR Experts:

Yes, you can tell nonexempt employees that they shouldn’t read or respond to messages when they’re not scheduled to be working. When communicating your expectations, it may be beneficial to investigate why these employees are checking email and messages outside their scheduled hours.

How you handle the issue may depend on what’s driving it. Employees feeling the need to catch up on work they didn’t have time to finish during their scheduled hours would likely have a different solution than employees deliberately clocking unapproved time to increase the size of their paychecks. If, after communicating your expectations, employees continue working unapproved time, you can remind or discipline them, as appropriate.

This Q&A does not constitute legal advice and does not address state or local law.