The Labour Party supports calls to rationalise the number of ports but opposes suggestions public assets such as the Ports of Auckland should be sold.
The party's transport spokesperson, Phil Twyford, says the country has too many ports and most are over-capitalised.
But he says the answer is not to privatise the ports nor to encourage Auckland and Tauranga to compete by driving down wages and casualising jobs.
Mr Twyford says selling a strategic asset such as the Ports of Auckland makes no sense and there needs to be a rational approach that protects New Zealand's long-term interests.
A Productivity Commission draft report released this month said port companies that are majority-owned by councils dominate the international transport sector and should be considered for further privatisation with partial stock exchange listings.
Transport Minister Gerry Brownlee says the commission is investigating airports and ports and will present a report to the Government in April.
Mr Brownlee told Summer Report any part privatisation of ports would be up the owners, not the Government.
"I think we have to have efficient ports and therefore we'll be very interested to see what sort of recommendations come out of the final report of the Productivity Commission."
He said rushing to any preconceived position would not serve anyone's interests.