Putting the GST on a carbon tax is inefficient and revisits the old era of hidden wholesale sales taxes, shadow treasurer Joe Hockey says.

News Ltd reported on Thursday that energy companies, waste disposal firms and appliance repairers are among businesses charging consumers GST based on carbon tax costs.

Mr Hockey said the "taxes on taxes" scenario revisited the pre-GST era of hidden wholesale sales taxes and would make the economy inefficient.

"The only area where you still have taxes on taxes is insurance which is the most hideous area of tax," Mr Hockey told the Seven Network on Friday.

"The best way to get efficiency in the economy is to have only one tax on a product, not an embedded tax and then another tax on top of it which is what's happening with the carbon tax."

But cabinet minister Tony Burke said GST charges have been levied in the same way since it was introduced in 2000.

"The mechanics of how the GST works across the entire economy have been set down for more than a decade now," Mr Burke told the Seven Network.

News Ltd reports that NSW electricity companies have confirmed the 10 per cent GST would be applied to power bills, after the carbon tax had been added to the bill.