NASHVILLE (AP) - Ask any restaurant server or bartender about side work and you are liable to get an earful. Sweeping floors, washing dishes, making salad? These are tasks that should pay minimum wage, but servers and bartenders routinely do them for as little as $2.13 per hour.

On Wednesday, a Ruby Tuesday server sued the restaurant chain claiming she is required to do excessive side work in a federal lawsuit she hopes will become a class action involving thousands of workers at 658 restaurants nationwide. The case is one of several, targeting some of the country's largest restaurant chains, filed after the U.S. Supreme Court in 2012 let stand a ruling allowing Applebee's employees to sue over side work. That suit ended in an undisclosed settlement with over 5,500 workers.

Ruby Tuesday, with headquarters in Maryville, issued a statement saying, "While we cannot comment on pending litigation, we are committed to our Ruby Tuesday team member s, and we will be providing a vigorous defense of the company on this matter in the appropriate forum."

Untipped workers at McDonald's, Taco Bell and other restaurants have made headlines recently with their "Fight for $15" campaign, demanding that the fast food companies pay them at least $15 an hour. And raising the federal minimum wage, now $7.25 an hour, has become the subject of debate among policy makers, with some states moving their rates to $15 per hour.

But the national minimum wage for tipped workers is just $2.13 per hour, a rate that hasn't changed in 25 years, although some states require a higher wage. Workers are allowed to be paid so little by their employers because tips are considered part of their wages.

Chris Hall, an attorney with the Ruby Tuesday case, said many tipped workers aren't aware of the Department of Labor rule that they should spend no more than 20 percent of their time doing untipped work like wiping tables and polishing si lverware.

According to the U.S. Department of Labor's Wage and Hour division, between 2013 and 2015, investigators found tip credit violations in over 1,500 cases, resulting in nearly $15.5 million in back wages.

But workers and advocates say many people are afraid to complain about problems.

Darron Cardosa, a server in New York City who blogs under the pseudonym "The Bitchy Waiter," said some side work is a necessary evil but it can easily become excessive.

"You just suck it up," he said. "If you complain too much, maybe you won't get as good a shift next week, or maybe you'll get sent home early."

It is illegal for employers to fire workers for complaining about labor issues "but they can find another way to make you regret it, or another reason to fire you," Cardosa said.

David Lichter is a Miami-area attorney representing 4,000 workers claiming tipped wage violations by the Darden restaurant chain - whose brands include Olive Garden, Lo nghorn Steakhouse, and, at the time of the suit in 2012, Red Lobster. The many individual complaints are still working their way through arbitration.

"These cases are not new and they're not uncommon," Lichter said. "Unfortunately, it seems to be a common practice in the restaurant industry. ...If you can pay sub-minimum wage for a job that would otherwise pay minimum wage you can make more money."

Teofilo Reyes is the research director with the Restaurant Opportunities Center United, which advocates for restaurant workers and pushes for tougher industry standards. He said seven states have eliminated the separate tipped wage - Alaska, California, Minnesota, Montana, Nevada, Oregon and Washington - and his group is advocating eliminating it nationally.

Reyes said the 20 percent rule can be difficult to apply because tipped work and untipped work can intertwine throughout the day.

"Eliminating the lower wage for tipped workers is the only way to ensure it isn't a problem," he said.

Kevin Dugan is the regional director with the New York State Restaurant Association. He said the 20 percent rule can be very difficult for employers.

"Restaurants would be better served if the laws were more specific about what constitutes side work," he said. "Certain things are open to interpretation."

But in general he said the lower tipped wage is important for many small restaurants that operate on a "very, very small profit margins."

Gabriella Santa, a college student who waits tables in Knoxville, said between busy days and slow days the money usually evens out, "but on weekday nights, when you're closing, and doing all this side work, and you've made only $20 in tips, and you're making $2.13 an hour - that's something anyone gets annoyed with."