Dear Rashmi,
Please try to find out the reasons why the employees are not coming in alloted shifts.Do share the same with us so that we can suggest you accordingly.
Alternatively you can prepare a format for Intimation of change in Shift Duty whereby the concerned employee, head of the department will sign the same and handover it in advance to HR Department, also a copy to be handed over to security gate for their information.Unless authorised by Head of department in this format and without intimation in this regard in the format dont allow the employees to change their shifts.Please communicate to all concerned departments that without intimation in the said format change in shift duty will not be considered. Please communicate the same to all heads and the top management also.Please also prepare a policy and procedure for change in shifts and get the same sanctioned by top management. Involve all concerned department members, departmental heads and seek their approval also.
You may also prepare a report reflecting the number of shifts changed by employees alongwith employee names in a particular month and send the same to the departmental head. Conduct meetings with the departmental members and heads to ascertain their issues so as to reslove the same.
Hope this helps.