Google co-founder Sergey Brin is backing a pair of ballot initiatives that oppose California’s controversial proposed billionaire tax in a high-stakes showdown ahead of the November election.

The two counter-measures — aimed as scuttling a proposed 5% levy on residents with assets exceeding $1 billion — would prohibit new taxes on a person’s financial assets and increase audits of programs funded by such taxes.

The group that authored the initiatives, Building a Better California, has benefitted from $57 million in donations from Brin along with $36 million from other billionaires and business leaders, The Wall Street Journal reported.

The first measure, which has collected about 1.4 million signatures, would prohibit new taxes on personal property, including retirement accounts, intellectual property and financial assets, while excluding real estate. It would also prevent those types of taxes from being applied retroactively.

The second measure, which has garnered about 1.5 million signatures, would increase audits of new taxpayer-funded programs and includes a provision that would essentially invalidate the proposed billionaires tax.

Poll results shared with The California Post show that 74% of voters support adding financial and performance audits to taxpayer-funded programs. A similar share of voters are in favor of prohibiting new taxes on retirement accounts and other property.

Both measure have more than enough signatures to land on the November ballot.

The union-backed billionaires tax — aimed at addressing funding gaps in state healthcare tied to cuts to Medicaid and other federal programs — had collected 1.5 million signatures as of last week.

Under California law, if competing measures pass, the one with the most “yes” votes prevails.

Polls indicate that about half of voters support a wealth tax. Gov. Gavin Newsom has opposed the proposed levy, arguing it would drive wealth and entrepreneurs out of the state.