Finance Minister Steven Joyce says the opposition are "dodgy on tax" but Labour says it's continuing to leave a number of tax issues open, saying they will be resolved by a tax working group after the election.
"They're refusing to say about the capital gains, they've mentioned a water tax last week, but they won't tell us how much it is, and then, of course, they've got a regional fuel tax they won't talk about where it goes beyond Auckland," Mr Joyce told TV3's The Nation programme on Saturday.
Labour's finance spokesman Grant Robertson wouldn't rule out a capital gains tax in the first term of a future Labour government because a tax working group would consider tax issues.
"I can't pre-empt what that group says, but here's the important point - right now today we have something called the bright-line test that the National Party brought in.
"It says that if you sell a house that's not your family home within two years, you'll pay tax on it."
He said that was a form of capital gains tax.
"What we're going to the election with is a commitment that if you sell a property that is not your family home within five years, you'll be taxed for that," Mr Robertson said.
Mr Robertson also would not rule out taking on the Green Party policy of a top tax rate of 40 per cent on incomes over $150,000 but said "I don't think we will be going for that".
Labour have been criticised for unveiling plans to charge for water without saying how much.
"The water levy? Look, what we've said there is for every thousand litres of water that's used in irrigation, perhaps one or two cents," Mr Robertson said.