High-income earners are set to see superannuation tax concessions cut in next week's budget.

The move to increase tax on concessional contributions to 30% is likely to affect the approximately 128,000 Australians who earn more than $300,000 a year.

Currently all concessional superannuation contributions are taxed at a flat rate of 15%, delivering a higher relative concession to those in the top income tax bracket, according to Bill Shorten, Minister for Superannuation.

''It is clear that a small number of people on high incomes are getting a better deal out of super than millions of Australians on average incomes,'' the Minister said on Friday.

''That's why we are making the system fairer, by ensuring that the tax incentives for super are more in line across income ranges," Shorten said.

"This will save a billion dollars to the bottom line and it will still provide a concession so that those who contribute to super will still be paying less tax by contributing to super than they would if it was just as their ordinary tax, which you pay for the rest of your income," the Minister said.

Workers earning more than $180,000 on the highest 45 per cent tax rate receive a 30 per cent tax concession on their super contributions under the current rate. It is understood those earning between $180,000 and $300,000 will continue to benefit from the current concession

Shadow Minister for Superannuation, Mathias Cormann has called the move a "tax grab".

"As of 1 July 2012, courtesy of previous Labor changes, higher income earners putting 9% of their income into superannuation already pay the top marginal tax rate for any super contribution in excess of $25,000," Cormann said.

"So Labor's suggestion that somehow higher income earners do not pay more tax on higher super savings is just not accurate."