Simon Bridges is pointing blame at Jacinda Ardern over the Commerce Commission's findings that New Zealand's fuel market is "not as competitive as it could be".
Bridges, leader of National, said while he agrees with the findings that New Zealanders are being ripped off, he said it's the Prime Minister who is to blame.
"The reality of this is that the biggest fleecer isn't the petrol companies - it's Jacinda Ardern and her Government," Bridges said ahead of his Caucus meeting on Tuesday.
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It was a reference to a comment the Prime Minister made in October last year, when she expressed concern over rising fuel prices, and said New Zealanders were "being fleeced".
"Jacinda Ardern is the Fleecer-in-Chief with all of the taxes that she's piled on," Bridges added, referring to the 3.5 cents per litre increase to the petrol excise tax in May - an addition to the increase in 2018.
"It's pretty simple: ultimately, you can't decrease petrol prices if you're putting up taxes," Bridges said. "Talk is cheap, petrol taxes aren't."
The Commerce Commission's study was undertaken after a request from Energy Minister Megan Woods in December last year to find factors affecting competition for the supply of retail fuel.
The findings released on Tuesday morning are preliminary and the full report will come out in early December.
The Prime Minister said on Tuesday that she wants to wait for the commission's full report before the Government acts on the findings. However, she said the Government is "ready to act".
"You will remember that our instinct was certainly that New Zealanders were being fleeced at the pump and now the Commerce Commission has confirmed that is true," she said before her Caucus meeting.
"They've confirmed that we have a problem, and they're now going to work on some of those solutions and we as the Government stand ready to act."
The commission found that there was a lack of competition in New Zealand's retail fuel market, and that it's dominated by the big players: Z Energy, BP and Mobil.
The companies use a shared network to supply 90 percent of the nation's petrol and diesel, either through their own branded service or via other distributors or resellers on exclusive wholesale contracts.
Without access to the main companies' shared network or the wholesale market, the commission said new importers would struggle to establish a standalone supply chain.
Woods said the issues raised in the report were identified by the Government hence her request in December for a review in the market.
"We need to go back and have a look at all those things but we also want to wait for the final report... But it would be remiss of us not to take that into account when looking at our options," she said.
The investigation was sparked by a spike in petrol prices last year. Between October 27, 2017 and September 28, 2018, petrol prices rose by 39 cents. Prices peaked at about $2.48 in October.
BP earlier this year argued that the cost of petrol prices are 44 percent made up of taxes, including excise duty, GST and ACC levies.
In a statement on Tuesday, BP said it has cooperated with the Commerce Commission, and will provide further comment after having read the full report.
According to the AA, a recent drop in fuel prices "was quickly reversed" with the scheduled tax increase on 1 July. It said the tax increase amounts to an extra $45 per year for the average motorist.
Bridges said while he accepts that there is a need for more "pro-competitive measures" in the fuel industry, the Government can't "make up for all these taxes with a bit of tinkering and talking around the edges".
ACT leader David Seymour had a similar take. He said he predicts the commission's findings will lead to more regulation of the market, but the same prices.
"Too much red tape and regulation prevents us from raising productivity."
Since 1970, National and Labour-led Governments have increased taxes on petrol about the same amount.
Ardern said she can give [New Zealanders] a "guarantee that we're not going to stand by while they continue to be fleeced".