As has been pointed above, VRS is for downsizing (viewed by the Unions) and rightsizing (argued by the Management) of workforce. However, for announcing any voluntary retirement scheme, the company has to follow certain procedures including getting approval from the Labour Commissioner. Also, the company should be able to prove that they have excess work force and that they do not plan to replace expensive workmen by cheap labour after the VRS. The minimum compensation to be paid is also laid down by the government whereas the maximum can be fixed by the Management in consultation with the Union to attract employees to opt for VRS. The Management has the right to accept or reject the application received from any employee, though in practise, most companies do not reject application received opting for VRS from any one.
Whether it is VRS or VSS, both are supposed to be voluntary in nature and any scheme offered for reducing the workforce coming under the bargainable category, has to be approved by the Labour Commissioner. However, companies tagetting specific employees do it quietly by offering compensation to targetted employees and asking them to resign or make them request for giving some compensation. The rules may differ from state to state marginally though.
Thanks for everyone who have responded with their comments as it is always good learning.