Labour leader Jeremy Corbyn says inheritance tax should be "graded" because the current single rate means the "very richest become richer".
He told the BBC's Andrew Marr Programme, a planned rise in the threshold amounted to a "tax break" for the wealthiest 60,000 families.
In his budget Chancellor George Osborne ended the 40% inheritance tax on family homes worth up to £1m from April 2017.
That was a rise from the current threshold of £650,000.
Mr Corbyn, speaking ahead of the Labour Party conference in Brighton, said: "The richest 60,000 families have suddenly had a tax break."
He added: "It should be graded actually. Somebody leaving a normal house to their children or family - fine. But when you cut the overall rate of inheritance tax that means that the very richest become richer because of it."
Mr Corbyn also said that the government is doing "very little" about companies that have moved their offices overseas for tax reasons.
He named Boots, which is headquartered in Switzerland.
He said that if a company is making a lot of money in Britain it "should pay tax on what they earn in Britain not by some piece of sophistry move it to Switzerland, Luxembourg or Lichtenstein".
In response a Boots spokesman told the BBC: "Boots pays all the tax that is due in the UK. It is a major contributor to the UK economy."
As for income tax, Mr Corbyn "hopes" to lower the rate for the least well off. But he said he had "no plans" to alter his proposals for a 50p top rate of income tax.