The White House unveiled a new “billionaire tax” as part of its $5.8tn budget proposal on Monday, as it sought to offset spending increases in areas such as defence and social care without raising taxes for ordinary Americans.

The proposal is the first time Joe Biden has offered a detailed policy to impose a tax on the wealth of the richest Americans. The US president has previously shied away from targeting billionaires directly, instead pushing for higher taxes on capital gains and companies.

The low effective tax rate applied to the ultra-wealthy has long been a political pressure point in the US. In a document outlining the new tax, the White House estimated that American billionaires pay just 8 per cent of their total income in taxes, while a firefighter or teacher pays double that rate.