Chancellor George Osborne could reportedly use next month's autumn statement to carry out a tax raid on rich individuals' pension contributions.
The Financial Times said Mr Osborne is "considering" reducing the maximum annual tax-free pension contribution below the current level of £50,000, after rejecting the Liberal Democrats' "mansion tax" proposal for raising revenue from the wealthy.
A new threshold of £40,000 would raise around £600 million a year for the Treasury, while a cut to £30,000 would deliver £1.8 billion.
The FT quoted unnamed officials as saying that moves to reduce tax relief on pension contributions were "on the table" at a meeting between the Chancellor and coalition colleagues on Monday.
As the December 5 statement approaches, the Chancellor is coming under pressure to balance his planned £10 billion squeeze on welfare with measures to hit the rich, to show the Government is sticking to its promise to ensure "we are all in this together".
Lib Dem calls for a mansion tax on properties worth more than £2 million failed to win favour with Prime Minister David Cameron, who believes it would be wrong to raise additional levies on the homes voters have worked and saved to afford.
An alternative scheme to charge more council tax on expensive homes has also apparently been ruled out after Downing Street said the Government had "no plans" to introduce higher bands for more valuable properties.
Another option still believed to be under consideration would be to increase stamp duty land tax on property sales worth £1 million or more, though this is expected to raise comparatively little money.
Adding 1% to sales between £1 million and £2 million would bring in about £70 million, while hiking the 7% rate for those worth more than £2 million would not yield much more, as there are relatively few deals of this size.