Big fuel users and motorists urged to top up now before fuel excise cut ends on Wednesday

The six month halving of the Commonwealth fuel excise ends on Wednesday night.

Treasurer Jim Chalmers last week said the end of the 22 cent cut to fuel taxes shouldn't trigger an immediate spike in prices on Thursday morning.

Dr Chalmers said fuel stations should have supplies in their underground tanks bought at the cheaper rate which should not attract the higher excise price.

But many still expect fuel companies will look to pass the price rise along quickly.

The federal government has tasked the Australian Competition and Consumer Commission to monitor the transition.

The former Morrison government halved the fuel excise tax for six months in its last federal budget in March after Russia's invasion of Ukraine caused global spike in the price of oil.

The new ALP government says the nation cannot afford to continue the cut.

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The fuel excise, or sales tax, was designed to fund road maintenance.

Dr Chalmers says the excise cut costs $3 billion every six months.

"We just can't afford to continue that relief indefinitely," he said.

Dr Chalmers said fuel prices "in most parts of the country" are now around 50 cents a litre below the peak recorded in July.

Diesel prices have not experienced the same sustained fuel price falls as unleaded petrol.

Australian farmers have access to the Fuel Tax Credit Scheme which means diesel used in paddocks to produce food does not attract the excise.

Dr Chalmers said there will be more than 700 million litres of lower excise fuel in the system when the fuel excise is reintroduced on Wednesday night.

The ACCC said fuel wholesalers are expected to pass on this lift in excise in full, from Wednesday night.

ACCC chair Gina Cass-Gottlieb said the commission would be monitoring wholesale and retail prices closely and would take action if retailers make misleading statements on price movements or if there is evidence of anti-competitive behaviour (such as price collusion).

She said the commission was watching for uncharacteristic or abnormal wholesale and retail price increases around the reintroduction of the full rate of fuel excise.

"Motorists are reminded that prices will continue to fluctuate with changes in international prices and the exchange rate, as well as petrol price cycles in the five major capital cities," Ms Cass Gottlieb said.

The ACCC recently said there was an average six-week lag among fuel retailers between when the excise relief was introduced and when that flowed on to cheaper fuel at the bowser, as retailers worked through existing stock bought at higher prices.

The ACCC said it expected a similar lag when the higher excise returns, and would be watching closely for retailers who may seek to take advantage of it.