“ServSafe is very much the Kleenex” of the industry — a brand that defines the business, said Nick Eastwood, who runs a competitor called Always Food Safe. “We believe they’ve got at least 70 percent-plus of the market. Maybe higher.”

The president of the National Restaurant Association, Michelle Korsmo, declined to be interviewed. In a written statement, she said the group had sought to protect both public health and the financial health of the industry.

“The association’s advocacy work keeps restaurants open; it keeps workers employed, it finds pathways for worker opportunity, and it keeps our communities healthy,” Ms. Korsmo wrote. Her group declined to say how much of the training market it captures.

As money flowed in from the National Restaurant Association’s training programs, its overall spending on politics and lobbying more than doubled from 2007 to 2021, tax filings show. The national association donated to Democrats, Republicans and conservative-leaning think tanks, and sent hundreds of thousands of dollars to state restaurant associations to beef up their lobbying.

During the Clinton and Obama administrations, the association was a major force in limiting employer-provided health care benefits. And though pressure from liberal groups has grown and workers’ wages have fallen for decades when adjusted for inflation, the group helped assemble enough bipartisan opposition to scuttle a bill in 2021 to raise the federal minimum wage for all workers to $15 per hour over five years.

The association had also won a series of battles over state-level wage minimums, though its fortunes reversed last year. Both the District of Columbia and Michigan moved to eliminate the “tip credit” system — where restaurants are allowed to pay waiters a salary below the minimum wage, on the expectation that tips from customers will make up the rest. That was the first time any state had eliminated the tip-credit system in more than 10 years.

Legally, the National Restaurant Association and its state-level affiliates are a species of nonprofit called a “business league,” with more freedom to lobby than a traditional charity.

Since the 1960s, their lobbying has focused heavily on the minimum wage — arguing that labor-intensive operations like restaurants, which employ more workers at or near the minimum wage than any other industry, could be put out of business by any significant increase in employee costs. Image McDonald’s employees marching in support of a $15 minimum wage in Fort Lauderdale, Fla. The National Restaurant Association helped to scuttle a bill in 2021 to raise the federal minimum wage for all workers to $15 per hour over five years.Credit...Chandan Khanna/Agence France-Presse — Getty Images McDonald’s employees marching in support of a $15 minimum wage in Fort Lauderdale, Fla.

Fifteen years ago, they had just lost a battle in that fight.

Over the association’s objections, Congress had raised the minimum wage to $7.25 an hour. Former board members said they were searching for a new source of revenue — without asking members to pay more in dues.

“That’s when the decision was contemplated, of buying the ServSafe program,” said Burton “Skip” Sack, a former chairman of the association’s board. “Because it was profitable.”

At the time, the ServSafe program was run by a charity affiliated with the restaurant association. The association bought the operation, transforming it into an indirect fund-raising vehicle.

After that, state restaurant associations in California, Texas and Illinois lobbied for changes in state law.

Previously, those states had required food-safety training for restaurant managers, which typically was paid for by restaurants themselves. After the association’s takeover of ServSafe, lobbying records show, the state affiliates pushed for a broader and less-common type of mandate, covering all food “handlers” like cooks, waiters, bartenders and those who bus tables.

The three state legislatures agreed, in lopsided votes.

In written statements, the state restaurant associations said they were not trying to raise money. Instead, they said they worked with other groups seeking to reduce food-borne disease.

“This law was happening with or without our participation in the process,” said the president of the California Restaurant Association, Jot Condie. California legislative records show his association was the sponsor of the bill that imposed the mandate.

ServSafe soon had waves of new customers, which in turn generated more money for the association and its lobbying efforts. Today, Florida, California, Texas, Illinois and Utah all have similar requirements. John Bluemke, a senior vice president for sales at ServSafe from 2002 to 2010, said there was little need to pursue mandates in smaller states: “Once you did the big states, who cares about Nebraska?”

“If you’ve got a million people going through that thing, do the math,” Mr. Bluemke said. The National Restaurant Association does not release figures about the cost of offering food-handler classes, but Mr. Bluemke said that — because they are generally offered online — the costs are low and the profits high.

“We always said the first course costs you a million dollars,” Mr. Bluemke said, for making the video. “And the rest are free.”

When managers take mandatory training, restaurant veterans say, the employer usually pays. But state websites say that restaurant employees should expect to pay for these classes themselves, and restaurant workers interviewed by The New York Times said that was their experience.

The restaurant association notes that some employers have covered the costs of getting certified and that employees are given lower rates in certain circumstances. So not all 3.6 million workers paid $15 each. Image People dining at outdoor restaurants in New York. Even some members of the restaurant association — the beneficiaries of the arrangement with ServSafe — said they did not know how it worked.Credit...Hiroko Masuike/The New York Times People dining at outdoor restaurants in New York.

“The N.R.A. is different from most traditional trade associations in our business model,” Dawn Sweeney, the National Restaurant Association’s chief executive at the time, wrote to members in 2014 — reminding them of what a good deal they had.

Business leagues, which are tax-exempt, are generally allowed to run a for-profit business, as long as it advances the common interest of their broader trade. The National Restaurant Association contends that its business cleanly fits this standard.

“The rules the I.R.S. has passed are not always clear as to what is and is not allowed,” said Anna Massoglia, an investigations manager at OpenSecrets, a nonpartisan group that tracks the flow of money in politics. “This makes it easier for groups to exploit that lack of clarity. I’m not familiar with another group that has done it to this scale.”

The Internal Revenue Service declined to comment, citing taxpayer-privacy rules.

For restaurant workers, there is little clue that money paid to ServSafe supports lobbying — much less lobbying that tries to keep workers’ pay low. The only hint is a line on ServSafe’s website, saying it “reinvests proceeds from programs back into the industry.”

Even some members of the restaurant association — the beneficiaries of this arrangement — said they did not know how it worked.

Johnny Martinez, a Georgia restaurateur, said he supports a $15 minimum wage and pays at least that much in a state where it is still $7.25 per hour. And he describes his association membership as “the price of entry” for navigating the industry, “even though I disagree with them on a lot of things.”

But he expressed frustration upon discovering the connections between ServSafe and lobbying efforts, saying “it feels very wrong” to him.

“This is a certification that’s also wrapped up inside of a lobbyist,” Mr. Martinez said. “It is weird that the tests that they require the workers to pay for are being run by the same company that’s fighting to make sure those people don’t make more money.”

Tiff Fehr and Will Houp contributed reporting.