Eric Schmidt is reportedly at odds with Google cofounder Sergey Brin over how a $100 million campaign against California’s billionaire tax is spent

Eric Schmidt and Sergey Brin helped build Google into one of the world’s most valuable technology companies.

Now, the former Google chief executive and the company’s co-founder find themselves on the same side of a California political fight—but a new report finds they are increasingly at odds over how to use their combined contributions.

The disagreement centers on the ultra-rich coalition that has spent more than $100 million trying to bring down Proposition 40.

The New York Post reported Sunday that Schmidt has grown frustrated with the anti-tax coalition led in large part by Brin after the group failed to prevent California Democrats from endorsing the wealth-tax measure.

The proposition, backed by SEIU United Healthcare Workers West, has notable Democratic Party leaders Bernie Sanders and Ro Khanna to champion it.

To add insult to injury, Propositions 41 and 42 were also shot down by the party—the party opposed the billionaire-backed counter-measures, though both still go before voters in November.

The party narrowly passed the endorsement threshold at 61.7%.

According to an advisor to Schmidt, the former Google CEO was not “irate” about the endorsement outcome.

Conversely, the advisor told Fortune that Schmidt’s “only current involvement in politics is his contributions to defeating the billionaires tax”—meaning the divergence stemmed from his contributions also being used to oppose other measures that had created the split between the former Google partners.

Schmidt and Brin have both contributed millions to the political organization Building a Better California to oppose Proposition 40.

But according to the advisor, the millions in funding are also going towards other areas, such as Proposition 45—an environmental policy —instead of solely focusing on barring the billionaire tax.

The Post suggests Schmidt’s internal dispute also stems from the coalition’s political effectiveness.

Despite millions in opposition funding, California Democrats endorsed the tax and killed opposing propositions.

That outcome contributed to Schmidt’s frustration with the campaign and its leadership, the report says.