Rachel Reeves could raise capital gains tax on sales of second homes and businesses to as high as 39% at this months budget, reports have suggested.
The Chancellor is said to be considering the hike from the current rate of between 20% and 28% for higher-rate taxpayers.
A Treasury spokesman said any reports on specific tax changes was “pure speculation”.
There is said to be growing concern about the limited options for tax rises to fill a hole the Institute for Fiscal Studies (IFS) thinktank says is as big as £25billion.
Speaking to The Guardian, one source said: “Some very big tax decisions are being left until very late in the day.”
Another told how the Treasury’s tax-raising plans were in “complete disarray”.
Ms Reeves and Sir Keir Starmer have repeatedly pledged not to raise taxes for “working people” by ruling out increases in income tax and national insurance.
A Treasury spokesman denied suggestions of plans being in “disarray”.
“These claims are inaccurate,” they said while adding that they did not comment on “pure speculation” regarding specific tax measures before a budget.