Fonterra says December should be a bumper month, but its exports could be hit hard by a strike at Ports of Auckland, at what is the worst possible time of year.
Exports are hitting their season peak, and Ports of Auckland agrees there could be delays if mediation on Tuesday cannot solve a dispute with the Maritime Union.
Six ships carrying cargo valued at $300 million have been diverted to Tauranga or Wellington, and two have been forced to wait in Auckland, this weekend.
KiwiRail has put on extra trains between Auckland and Tauranga to get the cargo to its destination.
The ports say they have managed so far, but a backlog will build up, the longer Ports of Auckland is out of action.
The Maritime Union is planning further strike action in the coming weekend if mediation on Tuesday is not successful.
Ports of Auckland spokesperson Catherine Everedge says the dispute will disrupt Fonterra's exports at the peak time of year, if it continues.
She says as soon as the port got the strike notice from the union they contacted Fonterra.
Ms Everedge says the port has been working with Fonterra, the shipping lines and other ports to try and minimise the impact.