Why Consultancy in Singapore are holding Employee's Salary for 3-4 weeks for final settlement after Leaving Company and how this can be avoided?

When any non-Singaporean employee leaves job or changes job in Singapore,he has to pay the Due TAX Amount plus Tax till Today to IRAS department.This is why Consultancy is withholding last one or two month salary of employee so that they can pay the TAX to IRAS department and after that return balance amount to employee.So,generally employee will get balance amount after 2-4 weeks depending upon consultancy to consultancy.Now,the question here is that why Consultancy in Singapore are holding Employee's Salary for 3-4 weeks for final settlement after Leaving Company and how this can be avoided?IRAS department generally takes 1-2 weeks of time to process the TAX once Consultancy submits IR21 TAX Form to IRAS department.This is where the problem is because IRAS department will process employee TAX only after they receive IR21 Form from Consultancy.Solution:According to MOM guidelines,Consultancy is required to file Form IR21 to IRAS department at least one month before last working day of employee.Most of the Consultancy are not following this guideline and holding the Salary of employee for 2-3 Week after last working day.So ideally Consultancy shouldn't wait for employee last day to file Form IR21 to IRAS department as it will delay the final settlement of employee because IRAS will take 1-2 week to process employee TAX only after they receive IR21 Form from Consultancy.So,every Employee has right to ask their Consultancy to file Form IR21 to IRAS department at least 30 Days before last working day.If this is followed and Consultancy submits Form IR21 to IRAS department before 2-4 Weeks of last working day,Employee will get their final settlement within 1-2 days after leaving Company.Employee don't need to wait 2-3 Weeks of time just for final settlement.