Prime Minister Christopher Luxon says raising the fuel excise tax and imposing an accommodation levy could be on the cards if National is re-elected.

On Sunday, the National party committed to three so-called Budget Responsibility Rules aimed at returning to surplus, cutting debt and keeping taxes low.

The party promised to adhere to them if re-elected as a bulwark against economic shocks, with Finance Minister Nicola Willis confirming there would be "no new taxes on working people".

Speaking to Morning Report, Luxon was asked what "on working people" meant.

He said it meant National wouldn't introduce the proposed taxes from the opposition, such as a "capital gains tax, a wealth tax, a death tax, a gift tax, an income tax, or company tax increases, and a land tax."

It was put to Luxon that most of those taxes weren't on "working people". Luxon replied that a capital gains tax would impact working people because "every business is impacted by that."

He said the extra costs end up being paid for by "working people."

Asked again what new taxes National would introduce, Luxon pointed to "existing policy" such as the fuel excise tax.

"That has been a long-standing levy that's been applied when you fill up at the tank, that's been in place for decades," he said, adding that the money was used to fund roads over successive governments.

The current government hadn't raised it over the last three years, but the tax is due to be raised on the first of January.

The government signalled in March it may put on hold its plans to raise fuel taxes next year, as it dealt with how to respond to the fuel crisis.

National campaigned on not lifting fuel taxes at all in its first term, which Transport Minister Chris Bishop maintained was "the right thing to do" in a cost of living crisis.

Instead, the government planned to bring in a 12 cents per litre increase from January 2027, followed by a 6 cents per litre rise in 2028, and 4 cents per litre in subsequent years.

Now, Luxon said it was "highly unlikely we'll do that" given the Iranian fuel crisis, "but at some point over that three-year term, we're going to need to lift fuel excise as we have always".

He also pointed to an "accommodation levy", which the government was already due to explore and had included in its regional deal with Auckland.

"We actually want to look at that," he said, and there were "a whole bunch of options we haven't landed on what that looks like."

"But we've said we're open to exploring that in [20]27 with the relevant cities that are under pressure with high numbers of tourists using infrastructure."

Luxon was also asked about announcing his plans to hold a referendum on MMP live on air last Thursday, and whether he'd made the policy up on fly.

"Well, I did feel sorry for my caucus colleagues because I was making the announcement on ZB, and then they're in front of media going across the tiles in Parliament."

Luxon's announcement blindsided his coalition partners and even appeared to catch his National colleagues off-guard.

MPs were unable to say whether it was National Party policy or just the prime minister expressing some thoughts, and were unclear on whether this was discussed with the caucus or not.

On Monday, Luxon said he was asked for his position, and there'd already been plans to ask New Zealanders about the "merits" of a four year parliamentary term.

"It just makes sense to ask the question about MMP and check in with New Zealanders."

He said it was "quite common" for party leaders to take positions on issues that get raised.

Asked if he was the right person to lead the National party into the election, Luxon said "absolutely".