Labour's foreign affairs spokesman Phil Goff is warning that the sale of the Pacific Forum Line may affect economic development in the South Pacific.
He says the shipping line jointly owned by twelve governments of countries in the Pacific is being marketed and the leading bidder is Sofrana.
"I believe there was a meeting in Fiji last week and one in Tonga next week will complete the process," Mr Goff said.
The New Zealand Government, through the Minister of Transport, currently holds 23.1 percent of the shares and 8.3 percent of the voting rights.
The Pacific Forum Line was set up in 1978 to provide competition in shipping services to the Pacific islands in a bid to keep freight rates at reasonable levels and foster island trade and economic development.
Mr Goff said he was concerned that if the line left government ownership and became simply a commercial enterprise it would no longer achieve the goals it was created for.
"What I'm concerned about is that there has been no public discussion and this will be presented as a fait accompli when the process is completed," he said.
The company runs four schedules, according to its website. One serves Fiji, Samoa, Tonga and the Cook Islands. Another serves Papua New Guinea, Solomon Islands and Vanuatu, while a separate service goes to the Republic of Kiribati and Tuvalu and another serves French Polynesia.