The Port of Tauranga's share price fell after Ports of Auckland announced that shipping line Maersk would resume its Southern Star service to Auckland, starting from July.
The Southern Star service moved from Auckland to Tauranga at the height of the port's bitter dispute with the Maritime Union in December, 2011.
"This new service, with bigger ships and larger exchanges of containers cements our position as the import port of choice," Ports of Auckland chief executive Tony Gibson said.
Gibson said in a statement that Maersk's return would require increased productivity "something our work over the last year has shown we can deliver''.
Ports of Auckland had been working to lift productivity by restructuring, improving processes, and by implementing a new shift and roster system for over a third of stevedores, he said.
The Northern and Southern Star is a two-loop, 10-vessel weekly service between Tanjung Pelepas, Singapore and New Zealand ports.
Five vessels deployed on the Southern Star service will be upgraded in the size of container they can carry, from the current 1900 teu (twenty-foot equivalent unit) to up to 2,800 teu.
By late trading, the Port of Tauranga's share price was down 14c, or 0.9 per cent, at $14.75.
One fund manager said the stock had weakened by about $1.00 over the last month in anticipation that Ports of Auckland would regain the Maersk contract.
In 2011, Maersk said industrial action at Auckland had played a part in its decision to take its business to Tauranga. The port said at the time the service amounted to nearly $20 million in annual revenue.
Ports of Auckland, which delisted from the NZX in 2005, is wholly owned by the Auckland Council. Port of Tauranga is majority owned by the Bay of Plenty Regional Council.