The AEEU and MSF unions want to merge to create a "super union".
The new union's aim would be to recruit 1 million new members, claimed the AEEU.
The new body would have a £1m recruitment budget in its first year, which would target under-unionised sectors such as IT and health. It would have an annual income of over £60m and assets of more than £100m. It would have a total membership of 1.1 million.
Roger Lyons, MSF general secretary, said, "Millions of working people in the UK have yet to enjoy the benefits of trade union membership and it is these people the new union will target."
The body would be the biggest affiliate to the Labour Party with over 100 MPs in its membership. It would represent members in firms like BAE Systems, Unilever, Pilkington and Rolls-Royce.
Ballot forms are being posted to members to vote this week.