A review of Road User Charges has recommended sweeping changes to the way the fee is collected.
It suggests axing the annual licence fee, and replacing it with a more expensive Road Network Access Fee.
But it doesn't recommend a diesel tax, as advocated by the transport sector.
Transport Minister Steven Joyce says the difficulty is that all the users agree the fund should remain the same size, but all argue their part of the cost should be reduced.
Mr Joyce says he has asked officials for further advice and he expects to hear back by June.