NZ First leader Winston Peters will push for container operations at Ports of Auckland moved north to Whangarei within 10 years if his party is part of government following next month's election.
He is due to outline the "cast iron" commitment at an economic development meeting in Wellington on Thursday, according to reports.
Auckland is contemplating the massive prospect of relocating.
Muriwai, the beach 40km northwest of Auckland, Manukau Harbour and the Firth of Thames have been suggested as alternative sites so the Auckland waterfront can be freed up.
Northland MP Mr Peters has suggested Whangarei's deep water port, 150km to the north, is a better idea if the Auckland-Northland rail line is upgraded.
"Aucklanders want their harbour back while Northlanders want the jobs and opportunity that would come from Northport's transformation," he told NZME.
"This is a cast iron commitment from New Zealand First but it needs New Zealand First to be in a pivotal position to demand it."
Mr Peters' plan involves stopping car imports through Auckland by 2019 and moving container operations to Whangarei by 2027.