Freighters say Aucklanders should prepare for food costs to rise, as the fuel tax bites today.

The Road Transport Forum's, Ken Shirley, says freighters will feel economic effects right away, and the costs will trickle down to consumers.

Freighter will be needing to negotiate increased freight rates with food providers and this will prompt a price increase for consumers right across the board, says Shirley.

Forklift operators, and forestry vehicle workers will also pay more to fuel up in Auckland today.

They're paying the 11 and a half cent fuel tax even though it's a tax to fund roading infrastructure that's not designed to catch off-road vehicles.

The government says they'll be able to claim that tax back through a rebate but Shirley says they're still in the dark.

"The whole regime of how those rebates will be claimed is not determined yet so there's a huge amount of confusion on how that will work," he says.