We’ve all been there. Maybe it’s when you grab a coffee in the morning or when you finish up a dinner out with friends. Maybe it’s when you least expect it, like at the merch table at a concert. You tap your card, only to be confronted with the dreaded tip screen. There’s a lot of talk about how much to tip and if you even should tip (more on that later), but why do we add gratuity in America in the first place?

Nina Mast has the answer. She’s an analyst at the Economic Policy Institute, a left-leaning think tank in Washington, DC. The point of the tip is to make up the difference between the minimum wage and the tipped minimum wage. “The tipped minimum wage is the lower minimum wage that employers can pay tipped workers with the expectation that tips will bring their pay up to the regular minimum wage rate,” she says. “Under federal law, the tipped minimum wage is $2.13 an hour. So tipped workers need to earn an additional $5.12 in tips to bring them up to the federal minimum wage, which is $7.25 an hour.”

On this week’s episode of Explain It to Me, Vox’s weekly call-in podcast, we find out how this system began and why we still have it.

Below is an excerpt of our conversation with Mast, edited for length and clarity. You can listen to the full episode on Apple Podcasts, Spotify, or wherever you get podcasts. If you’d like to submit a question, send an email to askvox@vox.com or call 1-800-618-8545.

Where does tipping in America come from in the first place?

Tipping goes back to the pre-Civil War times in the US. There were wealthy Americans who were vacationing in Europe, and they noticed this practice of tipping where if you had good service, you gave a small extra fee on top of what you paid.

Then, tipping started to fade as a practice in Europe but persisted in the US. We can tie that back to the abolition of slavery. Once slavery was abolished following the Civil War, workers who were formerly enslaved in agriculture and domestic service continued to do these same jobs, but employers didn’t want to pay them.

So instead of actually just paying them their wage, they suggested that the customer paid a small tip to Black workers for their services. That’s how tipping started proliferating across service sector jobs and became the predominant way that workers in these jobs were paid.

How did the restaurant industry start to do this?

It really goes back to the formation of the National Restaurant Association. From the very beginning, going back to the early 1920s, they united around a common goal of keeping labor costs low, essentially lobbying against any efforts to raise wages for tipped workers and to eliminate the tipped minimum wage.

It sounds like this whole policy is a direct legacy of trying to keep Black people from getting the same minimum wage as other workers. When were service sectors included in the national minimum wage?

It wasn’t until the mid-1960s that tipped workers got the same rights as other workers under changes to the Fair Labor Standards Act. In the mid-1960s — this is during the civil rights movement, a few years after the March on Washington, which called for stronger minimum wage protections — amendments to the Fair Labor Standards Act established a wage floor for tipped workers. It also increased protections for workers in agriculture, schools, laundries, nursing homes — a lot of sectors in which Black people were disproportionately employed and in which workers of color are still overrepresented even today. This was a big deal. Something like a third of the Black population gained protections under the Fair Labor Standards Act through these amendments in 1966.

Even after these amendments, the FLSA continued to exclude farm workers from overtime protections, and domestic workers didn’t gain rights until the 1970s. It was a significant change, and a big deal, for tipped workers to be covered, but there was a huge catch in the amendment. It established a lower minimum wage that tipped workers could be paid through the creation of the tip credit system. And that’s still what is in use today. This tip credit essentially allowed employers to count the tips that were received by their staff against half of the minimum wage that they were required to pay.

In 1996, the FLSA was amended again to raise the minimum wage federally from $4.25 to $5.15. Essentially, that froze the tipped minimum wage at $2.13 an hour, while the non-tipped minimum wage continued to go up. The tipped minimum wage has been stuck at $2.13 an hour since 1991, even though the federal minimum wage has been increased multiple times. And that’s still the situation we’re in now.

Why hasn’t this changed? It seems like it would be easier to give everyone the same minimum wage, and you wouldn’t have to worry about tipping.

I think that’s in large part due to the lobbying and advocacy efforts of the National Restaurant Association, its affiliates — groups like the US Chamber of Commerce — and other employer groups that have fought tirelessly to prevent the minimum wage from being raised, both for tipped workers and for other workers.

There is a proposal in Congress to raise the minimum wage to $17 an hour by 2030, and it would completely phase out this tipped minimum wage so tipped workers would receive the same minimum wage as everyone else.

Some states have already eliminated the tipped minimum wage, but a lot more states haven’t been able to do so yet. In most states, the minimum wage for tipped workers is still less than $4 an hour.

How does the tip credit system work in practice?

Employers are legally required to make up the difference if workers aren’t receiving enough in tips to get them up to the regular minimum wage. But in practice, it’s extremely difficult to enforce that rule. It’s largely left up to the workers themselves to track their hours, their tips, and make some complicated calculations about what they’re actually earning per hour per week.

Then they have to confront their employer if it seems like they’re not actually receiving the minimum wage, which obviously introduces a whole host of issues related to power dynamics. Not only is it difficult to calculate and keep track of, but it’s also difficult for workers to demand what they’re owed.

As a result, it’s largely not enforced. Workers who are already earning much lower wages than workers in non-tipped occupations are highly at risk of wage theft.

I think as consumers, we’re initially taught that tips are a way to reward good service. How should we think about tipping?

I think this is a big misconception. People don’t realize that they’re actually paying the lion’s share of their server’s wages through their tips. Unfortunately, when you fail to tip your server, you’re actually denying them their wage. We don’t have the luxury in the US of having the system that you describe where you can pay a tip for particularly good service or pay a smaller tip to indicate that you didn’t get good service.

How much do you typically tip?

I tip 20 percent as a standard, and sometimes, for a really good service, I’ll tip more. I think that’s basically the standard at this point in the US. It does get tricky, because we’ve seen a proliferation of tipping across lots of different transactions where a service wasn’t necessarily rendered.

I think customers are increasingly frustrated by that, especially as the costs of things have gone up. But I hope customers target their frustration not at tipped workers but towards the employers and the lobbying groups that have fought for decades to preserve and expand the system. When you’re tipping, remember that you’re actually paying your server’s wage, and that’s a problem that we need to be solving by putting the onus on employers to pay their workers.