There's a new policy disagreement brewing between Sen. Bernie Sanders (I-Vt.) and Hillary Clinton: a soda tax.

Clinton said on Wednesday that she supports Philadelphia Mayor Jim Kenney's proposal to pay for universal preschool using a soda tax.

"It starts early with working with families, working with kids, building up community resources -- I'm very supportive of the mayor's proposal to tax soda to get universal preschool for kids," she said at an event in the city, according to CNN. "I mean, we need universal preschool. And if that's a way to do it, that's how we should do it."

The Democratic mayor has suggested levying 3 cents in tax on every ounce of soda sold, according to The New York Times. It's not clear whether consumers or distributors would have to pay the tax, the city anticipates it would drive up the cost of soda.

Sanders responded to Clinton on Thursday by saying this plan would effectively tax low-income people, who tend to drink more soda than the wealthy.

"Frankly, I am very surprised that Secretary Clinton would support this regressive tax after pledging not to raise taxes on anyone making less than $250,000," Sanders aid. "This proposal clearly violates her pledge. A tax on soda and juice drinks would disproportionately increase taxes on low-income families in Philadelphia."

Kenney accused Sanders of siding with big businesses.

"I'm disappointed Sen. Sanders would ignore the interests of thousands of low-income -- predominately minority children -- and side with greedy beverage corporations who have spent millions in advertising for decades to target low income minority communities," he said on Friday, according to philly.com.

According to HuffPost Pollster, which aggregates publicly available polling data, Clinton leads Sanders ahead of Pennsylvania's Democratic primary on Tuesday.