More than 4,000 members of the Dairy Workers Union are planning industrial action against Fonterra, saying they want a share in the sector's success.
The union, which represents processing plant workers and drivers, is seeking a pay increase of 8%.
Fonterra and the union have failed to reach an agreement and will go into mediation next week.
If that is unsuccessful, the union says it will begin the first stage of industrial action from mid November, including limiting overtime and cover for absent workers.
National secretary James Ritchie says Fonterra is offering an increase of 5%, but farmers have had increases of 77% in their returns this year. He says the union will consider full strikes as a "last resort".
Fonterra says any industrial action that disrupts the processing of milk could have serious financial and environmental consequences.
