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.