The law requires the company to deduct and pay PF up to a salary ceiling of ₹15,000 per month. It does not prevent higher contributions, but the same must be by the consent of the worker. If the employee no longer wants to contribute more, a simple letter as a request is enough; there is no specified form. However, if the PF scheme itself stipulates that it will be based on the full salary (which often occurs with companies having their own PF Fund), the option to reduce the contribution may not be available. You need to verify the same.