The United Steelworkers of America (USWA) and the Paper, Allied Industrial, Chemical and Energy Workers International Union (PACE) have voted to merge.
The combined union would have 850,000 active members in 8,000 bargaining units in the US, Canada and the Caribbean. It would be the largest union in metals, paper and forestry products, tire and rubber, glass and energy.
The new union will be called the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union.
Members will vote on the merger at conventions next month.