The opposition movement is being partly funded by wealthy entrepreneur Stuart Smith, who revealed five people were on his mind when he put his financial weight behind the fight: his grandchildren India, Louis, Octave, Amile and Albertine.
Fearful over the legacy being left for his grandchildren - and everyone else's - he paid for two ads in the New Zealand Herald.
A plane towing a banner at the Stop Stealing Our Harbour protest, which will take place at Queens Wharf from 3.30pm, as well as two billboards in Parnell, were also funded by Smith.
"I've got grandchildren and the Auckland harbour is for future generations. It's not for today's generations and it's not for making money in a business.
"It actually makes more money as a tourist centre."
A port in Auckland was unnecessary, he reckoned, saying Tauranga or even Whangarei could meet the area's needs.
He had spent $15,000 to $16,000 to promote Stop Stealing Our Harbour so far.
"I would spend a lot more because it's quite a serious matter."
The group wants work halted until a study on the social, cultural, environmental and economic effects of the port's place in the wider city is completed.
Its open letter to Ports of Auckland stated: "The Waitemata Harbour is one of Auckland's greatest assets, one we hold in trust for future generations. Through your actions it is now under further threat. Aucklanders deserve better than this."
Smith founded the Smith Uren fabric agency in 1965, and it has grown to encompass a swath of companies that trade in textiles around the world.
While meeting the Herald on Sunday on Friday, he proudly pointed out a bus that had "our fabric" on its seats.
Smith described himself as a Wellingtonian until "there was a wind one day and I ended up in Auckland" and said he needed to do something with the wealth he'd amassed.
His philanthropy had already extended to children's charities and the Westpac Rescue Helicopter.
"You can't take the money with you when you die. I'd rather the harbour was still here."
The battle over the port extension was just beginning, he said.
"My ancestry is highland Scotland - we never give up."