Any rule or regulation formulated by the employer for the payment of gratuity that is more beneficial than the provisions of the Payment of Gratuity Act is valid and legal. In your case, the minimum service to be rendered by the employee is three years, which is less than the five years prescribed by the Payment of Gratuity Act. Therefore, there is nothing illegal in this. However, your scheme or rule or regulations should not be contrary to the provisions of the Payment of Gratuity Act regarding other conditions like the time of payment, circumstances under which gratuity could be forfeited, etc. If it is, then only those conditions/provisions which are less favorable than the provisions of the Payment of Gratuity Act will not be applicable, though the three-year rule will continue to be in force.
With regards,