But a spokeswoman for Treasurer Joe Hockey said this already happens.

On Saturday, the second of two yearly increases in the fuel excise will take place.

Indexed to CPI, it means the tax on petrol will rise by 0.3¢ per litre to 39.2¢. This means the tax has gone up by more than a cent a litre since the government reintroduced indexation in November last year.

Indexation stopped in 2001 at 38.1¢ a litre but it was reset at 38.6¢ last year, and increased to 38.9¢ a litre in February.

NRMA director for the Illawarra Marisa Mastroianni said the government needed to ensure at least half the fuel tax revenue collected went towards roads funding.

Ms Mastroianni said an average of 32 per cent of the fuel tax was returned to the road network between 2004 and 2014.

"We want to see a stronger commitment from the Government for long-term funding," Ms Mastroianni said.

"Motorists have been hit with a double tax whammy: they already pay GST on top of the petrol tax. This hip-pocket hike would be easier for our members to take if more was going back into vital roads and public transport.

"The only guarantee we've had is for a one-off $1.1 billion injection for the Roads to Recovery program, which is good, but it's not enough."

A spokeswoman for Mr Hockey said road funding was already on their radar.

"All the revenue raised through re-indexing fuel excise will be linked by law to funding roads," the spokeswoman said.

"It provides a source of revenue to enable the government to deliver its historic infrastructure growth package of over $50 billion - the biggest infrastructure spend in the history of the Commonwealth.

"The agreement to re-index fuel excise also included an additional $1.1 billion for the Roads to Recovery program over the next two years.

"Total Roads to Recovery funding is $3.2 billion over the five years to 2018-19.

"This money goes straight to local councils to upgrade and repair local roads according to their own priorities."