The overall gender pay gap has been well-documented, but a new report shows it's particularly pronounced in the food service industry, where women are being underpaid in just about every job--even when accounting for tips.

The median hourly wage paid to women is less than it is for men in all but one of the eleven jobs surveyed in a report by the Economic Policy Institute. In some cases, the gap is slight—for cashiers, dishwashers, food preparation workers, and hosts and hostesses, it's a matter of cents. But in others, including supervisors and bartenders, the difference is well over a dollar. For managers, the highest earning occupation, the disparity was nearly three dollars per hour.

"This is what we identify as pay discrimination," said Valerie Wilson, an economist at the Economic Policy Institute. "The work women are doing is being valued at less than the work men do in the same job."

Women, however, aren't merely being paid less to do the same job—they're being paid less and less compared to men as they move up in the ranks, too. Some of the highest earning occupations—managers, bartenders, and supervisors—are also the ones with the largest gender pay gap.

"As you go up in the pay scale, that's where these gaps tend to emerge, that's where we're seeing the most of the difference," said Wilson.

The reason the divide grows more severe as the job becomes more important is unclear. There is some evidence that the trend is partly due to that fact that women, in many cases, take time off to raise children, and in doing so lose time that is akin to experience. There's also the possibility that men are, for whatever reason, simply more willing to negotiate with employers about money, and ask for a raise.

But even if those reasons hold any merit, experts say they still don't explain the extent of the disparity. "These aren't good explanations for why the pay gap exists," Wilson said.

Rather, the gender pay gap more likely has to do with other, systemic forces. There aren't laws that govern what people make at the top of the pay scale. For workers making near minimum-wage, the potential for disparity simply isn't large; for those making well above it, the potential is vast. Workers also don't typically know what someone else doing a similar job makes. What that means is that it isn't just difficult for a woman to prove that she's being underpaid—it's hard to even know she's being underpaid in the first place.