Why a vote on taxing California’s billionaires is being watched around the world

US independent senator Bernie Sanders at the launch of the campaign for the California Billionaire Tax Act.

Patrick T.

Fallon/AFP via Getty Images In November, California will vote on a proposal to levy a one-off 5% tax on the wealth of all billionaires in the state.

Google co-founder and billionaire Sergey Brin has already spent US$100 million on political donations to a group opposing the tax.

Brin is hoping to avoid a potential tax bill of US$13 billion, a return of roughly 130 to 1 if that investment is successful.

Advocates of the billionaire tax claim it would raise US$100 billion in revenue, to be allocated directly to state-funded healthcare, food assistance and public education.

Supporters of the union-backed proposal also highlight that most billionaires currently pay lower marginal rates of tax than the average worker, and that the revenue is desperately needed to fill gaps in funding created by US President Donald Trump’s cuts to Medicaid.

Its critics, which include California’s Democratic Governor Gavin Newsom, argue the measure will drive billionaires and their tax revenue to leave the state.

Taxing the ultrawealthy Similar measures targeting the ultrawealthy are currently under consideration around the world.

In New York, Mayor Zohran Mamdani has proposed a 2% income tax increase for those earning over US$1 million, and passed a property surcharge tax on second homes.

Other US states – including Washington state, Maine and Minnesota – have passed or are considering similar income or wealth tax measures.

In the United Kingdom, a group of 120 millionaires have launched a “Proud to Pay” campaign asking the government to levy an additional 2% tax on wealth over £10 million.

Spiralling global inequality Behind the public discussion of California’s billionaire tax lies a much deeper debate about spiralling global inequality.

Recent data from the US shows the share of economic output flowing to workers has dropped to a record low of 52.9% in 2026.