Google co-founder Sergey Brin has contributed approximately $45 million to oppose California's proposed wealth tax on billionaires, according to reports. Brin's funding goes to a group called Building a Better California, which is campaigning against the tax measure.

The opposition campaign is spending heavily to collect signatures, reportedly paying $15 for each valid signature obtained. This represents a significant per-signature cost in what has become an expensive political battle over the proposed tax.

The proposed tax would target California's wealthiest residents, though specific details of the measure were not provided in available reports. The initiative has drawn opposition from Silicon Valley's tech elite, who view the tax as potentially harmful to the state's business climate.

California has previously considered various wealth tax proposals, though implementation has faced legal and practical challenges. The state already has some of the highest income tax rates in the nation, particularly affecting high earners.

The campaign represents part of a broader national debate over wealth taxation and income inequality. Several states have explored similar measures targeting ultra-wealthy residents, though few have successfully implemented comprehensive wealth taxes.