P.F compliance by Principal Employer


I have the following 2 questions concerning P.F liability on the Principal Employer:

  1. Suppose an establishment has employed less than 20 employees and their Basic wages are more than Rs. 15000 per month but has engaged multiple contractors at its construction site for a construction project and the total no. of such workers is more than 20, should the establishment register itself under P.F and file nil returns?
  2. If a Principal Employer is registered under P.F and engages an independent contractor whose total employee strength is less than 20, then should the contractor obtain a P.F registration and remit P.F for his employees or what is the P.F liability on the principal employer in this case?