Tax concessions promise to be a flashpoint at the next federal election after Labor announced a 30 per cent tax rate on superannuation earnings for balances above $3 million, but not until 2025, after voters have gone to the polls.

While the change will affect 80,000, or just 0.5 per cent of savers, Treasurer Jim Chalmers said the $3 million cap would not be indexed, meaning younger generations would increasingly be locked into higher taxes on their retirement savings.