Bernie Sanders, the senior United States senator from Vermont, accused billionaires like Elon Musk, Mark Zuckerberg, and Sergey Brin of spending millions to kill a ballot measure instead of “paying their fair share.

The senators want the Government Accountability Office to investigate.

In Durham, he’ll be joined by County Commissioner Nida Allam, a progressive Democrat challenging U.S. Rep. Valerie Foushee.

Sanders wrote on social media that he strongly supports the tax “at a time of unprecedented and growing wealth and income inequality.”