There’s no limit per se, but there are few factors you might want to consider:

• If the employee was looking for a part-time job when you hired them (and didn’t settle for fewer hours than desired), you may get pushback if you assign more hours than they bargained for on a regular basis.
• Under certain laws, as well as insurance and retirement plans, benefits kick in when an employee hits a certain number of hours per week, regardless of how you classify them. For example, the Affordable Care Act (ACA) considers employees full time at 30 or more hours per week.
• If you regularly assign an employee a full-time schedule while continuing to classify them as “part time”—and full-time employees receive additional benefits, such as paid time off—the employee could argue they’re being treated unfairly or even in a way that amounts to employment discrimination.

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