JULIA Gillard has been warned not to mess with the diesel fuel rebate in her carbon pricing scheme.

The Prime Minister will reveal details of the carbon tax on Sunday but the opposition's warned her today that she'll be in for a fight if she changes the diesel fuel rebate for farmers or concessions for off road vehicles.

Nationals senator Fiona Nash says the PM will face the wrath of regional Australia if that arrangement changes because the carbon tax will hit farmers and regional communities the hardest.

Senator Nash was speaking on a private bill which aims to force a plebiscite on the carbon tax to be held no later than November 26.

But Labor senator Doug Cameron has dismissed it as a political stunt from climate deniers in the opposition.