If an employee leaves the job without clearing the dues, there are two options:
1) Notify him/her to clear the dues so that a relieving letter may be issued. If the employee does not respond to such notice, then -
2) Recover the dues from his/her terminal dues payable to the employee.
Legal Action for Unpaid Dues
If the employee has no payable dues and is not responding to the notice as at (1) above, then if the amount is considerable, a legal notice is the only solution. If the amount is negligible, then it is better to consider it as bad debt with the competent approval instead of spending more than the amount on the recovery of it.