Dear,
Are we talking about the workman category who comes under the purview of the Industrial Disputes Act, 1947? If yes, the probation period shall be as per the Model Standing Orders of the State. Even if you have certified standing orders, the probation period can't be more than the period mentioned in the model standing orders of the state. Normally, it is six months which can be extended up to one year maximum.
If it does not fall under the ID Act, 1947, then as per the service rules of the company/as per the terms of the letter of appointment.
Ak Malhotra Sr General Manager