Hamilton City Council will "conditionally oppose" Watercare's request to take more water from the Waikato River for Auckland.
Mayor Paula Southgate said Hamilton councillors "have to put our city first and ensure Hamilton's interests are also well looked after" in Watercare's bid to take an extra 150 million litres of water a day from the river.
"Auckland, like every other centre in New Zealand, must consider the future sustainability of its water supply," she said.
"Water is gold and the Waikato River can't be all things to all people."
Hamilton already takes water from the river to look after its 180,000 residents. The city's current consent for water ends in 2044.