I.D. Act, 1947

Absolutely not. Mine is a factory manufacturing different engg. parts. I was clarified that Sec. 25-N is applicable to my own factory employees not to the contract undertaking which I employed in my factory. My manpower contractor's establishment does not fall within the three classifications Factory, Mine or Plantation.Therefore, I put forward my query once again if it is not applicable what's the procedure for retrenchment he has to follow statutorily under ID Act as ID act covered contract establishment also? Or if the advise given to me was wrong and the contractor has to go for prior permission from the Government? Pl.advise.

I think there is a disconnect right there.
If a contract worker is working in your factory, then he is a part of your establishment both for factories act and ID Act. It does not matter that the contractor has a different office. Since sec 25N applies to your factory it applies to all those who work there irrespective of who pays their salary.
If the contract workers are working in the contractors factory, then this matter does not apply to you at all. Why should you worry about someone else's factory.