Is PF Contribution Mandatory for Employees Earning Less Than 6500? Seeking Advice

Can anyone help me? I am working as an HR officer in a software company. The employee strength is 21. Five employees (Basic + DA) have a salary of less than 6500/-. However, they do not want to contribute to PF due to some personal problems. I want to know if the employee is bound to pay PF or not. Is there an option for PF exemption for those whose Basic + DA is less than 6500?

They have to be covered and are required to contribute. There is no way to exclude them. Think of a newcomer with less than $6,500 and willing to contribute...

With warm regards,
S. Sethupathy