Venkat,
Unfotunately all we feel that union is an obstacle and head-achque but it is an advantage. Only the thing that you should no chess game ie., you should know a bit in advance about their move, then you are a master.
Don't play a foul game of encouraging the other group to form one more union until and unless they work on their own. You will be sand-witched in between, you should be very careful why because over a period of time like our MLAs these people will also jump in to the other group and they will share what happend in their previous group and if both comes to know about your interest then it is going to be a hell for you and there is no other alternative for you except quitting the job.
It is easy for you to negotiate with a team of 5 member instead with all the individual employees. once you complete the long term agreement ie., 3 / 5 years you purchased peace for that period and no negotiations till the end of the term etc etc are the benefits. If you want more info pl. forward your requirement to my ID

Regards - kameswarao