As you are already in HR, I won't elaborate much on the concept of dual employment. Typically, employers do not allow full-time employees to engage in dual employment due to the need for undivided attention to their primary job and the safeguarding of their business interests. While it may not be explicitly stated in the employment contract, it is generally understood that a full-time employee should not work for another employer concurrently, especially in the same industry.
Therefore, my advice to you would be to cease this practice immediately.