Former Google chief executive Eric Schmidt has reportedly soured on the political coalition fighting California's proposed wealth tax, after state Democrats endorsed the measure despite a well funded opposition campaign, Fortune reported, citing the New York Post.

An adviser to Schmidt pushed back on the characterization that he was furious about the outcome, telling Fortune his involvement remains focused on defeating the tax itself rather than any internal rift with fellow billionaire Sergey Brin, who has led much of the opposition effort.

Schmidt and Brin have both funneled millions of dollars into Building a Better California, a political group fighting the proposal, known as Proposition 40, which would impose a one time five percent tax on the net worth of state residents worth more than a billion dollars. Brin has provided the bulk of the group's funding, which also backs related measures aimed at auditing how any wealth tax revenue would be spent.

The pair are not alone in opposing the measure. Fortune noted that other wealthy figures, including Mark Cuban, have publicly sparred with California lawmakers over the proposal. Schmidt, who ran Google from 2001 to 2011 and later served as its executive chairman, has an estimated net worth in the tens of billions of dollars and did not respond to Fortune's request for comment.