The Labour Party's tax package to be unveiled next week is expected to contain a capital gains tax for investment properties.
However, leader Phil Goff is refusing to give any details until the policy launch on Thursday next week.
In Parliament on Tuesday afternoon, Prime Minister John Key continued to speculate about the contents of the tax package.
He told the House a land tax would see house prices fall and a capital gains tax would see more New Zealanders heading overseas.
Radio New Zealand understands the centrepiece of Labour's economic policy will be a capital gains tax, with the family home exempted at a rate of about 15%.
Labour has already announced some aspects of its tax policy - no tax on the first $5000 of income, no goods and services tax on fruit and vegetables, and likely tax increases for top earners.