The bane of Unionisation in India is mainly the ideological differences between Management & Union. We have seen many of the demands could easily be addressed provided management will take a flexible stand on certain trivial & just demands as per applicable acts. That's not happening in India. Both Union office bearers and Management have toe only ego clashes between them and with the result none is understood each other. A go-getter achieve most than the other. I suggest you should study the IR models the TATAs are adopting, frankly I don't see much of disturbance in their units.
Coming to your position, being an officer you have no role to play in the Union therefore you can at best give strategic inputs and guidance without straining the rapport with management. Most of the tiffs are related to wage revision and bonus issues. All other issues could be amicably settled if they are not eating into resources of the Co too much.
I don't suggest you should sign this letter. If this is a recognised Union & as a single bargaining agency under the TU Act, it's just to allot a suitable room for union activities and a formal letter may be signed by the President himself, where is the necessity that only GS should sign. If the bye-laws says so then amend it for authorising the President to sign all communications. If you continue to be GS, you should immediately resign by severing all official involvement with union. Going by past deeds of yours no one would believe that you no more have any truck with the union,that tag will continue to linger on you. Nonetheless you might continue to extend your suggestions and advices if you wish and safe guarding yourself from punitive action by management will only depend on how you are going to camouflage your efforts in sensitive issues. In all these efforts your success or not will be influenced by hardliners in the ranks. Nowadays threats from unions are not taken that seriously. If management is determined union activities can be silenced effectively.
29th November 2018 From India, Bangalore