How should we handle exempt employees’ sick leave taken under our PTO plan?

Q. The FLSA requires that we pay the full salary for any week in which the exempt employee performs any work. We have a sick leave plan for all employees included in our paid time off—or PTO—plan. If an exempt employee calls off sick, we dock her PTO available, which includes sick or vacation. In other words, our PTO isn’t split into sick and vacation pay. Can we dock this bank until it’s gone before we pay her for nonwork days?