Answered by the HR Experts
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.