The Public Service Association, which has 55,000 members, and the Service and Food Workers Union with more than 20,000 members are exploring the possibility of merging.
PSA national secretary Richard Wagstaff says the two unions already work side by side in a number of areas, including the health sector, and joining forces could provide many benefits.
Mr Wagstaff says it may be months before a decision is made on whether a merger will go ahead.
The Public Service Association is the largest state sector union in New Zealand.
