Yes, you can send employees home early due to a lack of work. Just keep in mind that exempt employees would need to be paid their entire salary for the day. Non-exempt employees would only need to be paid for actual hours worked, unless you operate in a state with reporting time pay requirements.
If you do operate in a state with reporting time pay requirements, employees may be entitled to reporting time pay for a certain number of hours even if they just show up and do no (or very little) actual work. This pay requirement is intended to lessen wage loss that is not the fault of the employee, as well as encourage employers to not over-schedule, since overscheduling and then cancelling shifts causes employees to waste time and resources getting to work. Given this, some employers decide to keep employees on the clock for more or all of their shift even though business is slow.
States with reporting time pay include California, Connecticut, Massachusetts, New Hampshire, New Jersey, New York, Oregon (for minors), and Rhode Island; the District of Columbia also has reporting time pay. The requirements for each of these states can be found in the Laws section of the HR Support Center.
Answer from Angela, SPHR: Angela has extensive experience in HR, conflict management and employee relations. She spent several years working as a high volume (and full cycle) recruiter for a large multi-channel retailer. Angela earned her B.A. in English Literature and Criminology from the University of South Florida and also holds a paralegal certification from Saint Petersburg College. Angela also is certified to investigate Federal sector EEO claims of discrimination.