It's illegal in principle! Being a supervisor itself is invited by Party A to supervise and manage the construction unit, and you are working in a part-time construction unit of this project, so you are suspected of "colluding with the construction unit"! However, on the other hand, you have done a good job, and your name is not on the materials you helped the construction unit. Who will help you pay the bill? If you do it, you do it. No unit can check this for you!