The New Zealand government pressed ahead with its controversial sell down of state-owned assets Monday, putting a 20-percent stake in national carrier Air New Zealand on the market, as the country readied for a referendum on the issue.

The Electoral Commission announced Monday that 3 million referendum papers would begin arriving at homes around the country this week, asking voters the question "Do you support the Government selling up to 49 percent of Meridian Energy, Mighty River Power, Genesis Power, Solid Energy and Air New Zealand?"

Voting in the postal ballot closes on Dec. 13, and although it is non-binding, it is being seen as a crucial test of the government's claim to have a mandate for the sales, which were announced before the 2011 general election.

The government has already gone ahead with the partial sales of electricity companies Mighty River Power and Meridian Energy, while the sale of mining firm Solid Energy has been put on hold indefinitely while the company struggles with huge debts.

On Monday the government began its two-day sale of shares in Air New Zealand, just a day after officially announcing the offer.

It owns 73 percent of Air New Zealand, unlike the 100-percent state-owned energy companies, and was reportedly pitching the shares at an opening price of 1.60 NZ dollars (1.34 US dollars).

Air New Zealand requested trading of its shares on the New Zealand and Australian stock exchanges be suspended until the bookbuild process was completed.

The government, which claimed it was confident of achieving at least 85-percent New Zealand ownership of the shares for sale, said the timing of the sale was right as the airline's share price had recently been trading at five-year highs and was up about 25 percent over the past 12 months.

However, critics claimed the timing, just as the referendum was getting underway, was deeply cynical.

The opposition Green Party said the leaking of the Air New Zealand sell down last week showed that selected financial institutions, rather than the government's target of so-called " mum and dad investors," were being given inside information by the government.

"Just 2 percent of the public bought shares in Mighty River, only 1 percent bought into Meridian, and, for Air New Zealand, that figure will be zero percent," Green Party co-leader Russel Norman said in a statement.

"This is a cynical attempt to flog off an asset to big institutions just before Kiwis get to have their say on asset sales. It is an insult to the 327,000 Kiwis who put their names to the petition that triggered the referendum and the vast majority of New Zealanders who oppose asset sales," said Norman.

Public opinion polls have consistently shown overwhelming public opposition to the sales program.