Warren Buffett to join Hillary Clinton on Nebraska stump

Hillary Clinton
Randall Hill | Reuters

Billionaire investor and outspoken Hillary Clinton supporter Warren Buffett will stump with the Democratic contender in Omaha on December 16.

In news first reported by the Omaha World Herald, the event is part of an effort to mobilize grassroots support for the candidate in advance of the state's Democratic caucus. According to the report, Clinton is expected to talk about tax reform with Buffett, who has publicly called on higher taxes for the wealthy.

A spokesperson for the Clinton campaign confirmed to CNBC that both Clinton and Buffett would appear together in Nebraska next month.

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Last year, Buffett said at an event that he was willing to "bet money" on the fact that Clinton would be elected president in 2016.

Yet the investor, who consistently ranks among the world's wealthiest men, has also had kind words for Vermont Senator Bernie Sanders, the socialist who is currently one of Clinton's challengers for the Democratic nomination.

The Oracle of Omaha has also long been a proponent of higher taxes on the wealthy. A few years ago, Buffett called for a "Buffett Rule" that would apply a minimum 30 percent tax on those making a million or more a year, and 35 percent on incomes over $10 million.