The Venn diagram of policies on which Donald Trump and Kamala Harris agree resembles two different circles, but not quite. Both leading candidates support eliminating the federal tax on tips.

This could attract the vote of tipped workers, who make up 2.5 percent of the American workforce, but what would this mean for tax policy?

More than a third of tipped workers — including restaurant waiters, bartenders and hairdressers — have incomes so low that they already pay no federal income tax.

“So if someone’s tax liability is already zero and you want to reduce that tax liability, you can’t go any lower,” says Bridget Stomberg, an accounting professor at Indiana University.

There are concerns that this tax policy would treat workers with similar incomes differently, she said.

For example, “You make $32,000 a year as a cashier and I make $32,000 a year as a waitress, and part of my income is tips and none of yours is tips. All of a sudden I’m paying less in taxes than you – just by virtue of the fact that I’m a waitress and you’re a cashier,” she said.

And it could lead to more people wanting to swap their job as a cashier for a waitress.

“I would expect the restaurant industry and industries where tips are an important source of income to see more interest from workers if this were to become law,” said Garrett Watson, a senior policy analyst at the Tax Foundation.

The Tax Foundation estimates that eliminating the income tax on tips would cost at least $107 billion in revenue over ten years.