Labor MP Eddie Hughes has labelled the state government's potential tax increase to outback communities as "mean and nasty", calling for it to be ruled out.
Under a new schedule of charges for 2019-20, property holders north of Port Augusta could be hit with a $100-$400 levy per property per year.
The new tax will affect outback areas where there's no council, with the funding to be directed to the Outback Communities Authority to maintain services and upgrade infrastructure.
The Marshall government is also considering dumping its vehicle registration fee concessions for Kangaroo Island, Coober Pedy and Roxby Downs - and in any regional area where there's no council.
Shadow Minister for Primary Industries and Regional Development Eddie Hughes said the tax has been sprung on these small communities "completely out of the blue".
The increase was buried in a state government announcement regarding higher fines for hoons and motorists on mobile phones.
"This is the worst time ever to be contemplating a new tax on pastoralists and land owners who are experiencing shocking conditions because of the drought," he said.
"Reports today show in some part of the state it has been the driest January to May period on record.
"Taxes, funding cuts and privatisations are not the answers to running our state."
The price hike comes as part of the state government's response to offset the enormous $517 million write-down in GST revenue.
Treasurer Rob Lucas said the increases follow an average rise in fees and charges of 3.1 per cent over the last two decades.
Most of the proposed increases are by 5 to 10 per cent, while the the standard indexation factor is currently just 2 per cent.
"It's no secret the state faces a significant $517 million shortfall in GST revenue in 2019-20 and it's imperative we seek to plug that hole in a responsible way. The Government will continue to cut waste and reduce spending in lower priority areas and increase revenue, especially from people who are breaking the law,'' said Mr Lucas.
"We're cracking down on lead-foot drivers of company cars who speed and run red lights."
But the Opposition has described the property tax as "sneaky", calling for the state government to find an alternative way to fund the Outback Communities Authority.
"Steven Marshall has broken his promise to deliver lower costs. What's worse, he's taking money away from country South Australians - many of whom voted for him based on the Liberals' empty catchphrase 'regions matter'," Shadow Treasurer Stephen Mullighan said.
"Steven Marshall doesn't care about regional South Australia, all he cares about is taking money from regional SA."