NEW YORK — Danger and exhaustion came with the job in the decade Chen Tianyun spent as a restaurant delivery man in Manhattan.

Traffic threatened to squash his scooter like a dumpling. He survived an armed robbery. Most weeks, he toiled 70 hours so he could send money to his family in China.

And for his efforts, he said he was paid a salary of $550 per month — about $1.81 per hour.

Live on your tips, his bosses told him.

Stories like Chen's are a dime a dozen in New York City, where immigrants make up nearly half the workforce, and employers who ignore labor laws have long been able to count on a complicit silence from laborers thankful for a job.

But lately, many of those arrangements have been threatened by a simmering service-industry rebellion.

In recent years, low-paid workers nationwide have filed a growing number of lawsuits seeking thousands of dollars in back wages from bosses they say failed to pay the minimum wage or overtime.

The complaints cover a wide range of industries and workers, from landscapers and warehouse laborers, to shop clerks and construction contractors. But most share a common trait: They involve immigrants who have become bolder about going to court to demand their proper pay, regardless of their legal status.

Some of the business owners being sued insist they treated workers well, and are themselves being taken advantage of by savvy activists and attorneys.

Federal lawsuits alleging violations of the Fair Labor Standards Act have more than doubled nationwide in recent years, rising from 1,854 cases in 2000 to 4,389 in 2006, according to the Administrative Office of the U.S. Courts.

MOSTLY LIVING ON TIPS

In New York, many of those complaints have come from workers who say that, for years, they worked mostly for tips.

Chen and fellow delivery workers at the Saigon Grill, a small chain of Vietnamese cafes, filed a lawsuit seeking back pay in March. More than a dozen New York restaurants have seen similar claims in the past few months.

Grocery baggers at supermarkets in low-income neighborhoods have filed lawsuits and complaints with state labor officials over the past year, claiming their only pay was handfuls of coins offered by customers that sometimes added up to as little as $250 a week.

In the South, the Southern Poverty Law Center has filed suits on behalf of Mexican and Guatemalan forestry workers — in the U.S. legally on guest-worker visas — who claim to have been denied overtime and effectively paid less than minimum wage.

On the hurricane-ravaged Gulf Coast, the poverty law center and the National Immigration Law Center have brought similar suits on behalf of foreign-born workers who took construction and cleanup jobs, only to find that they paid far less than promised — or, in some cases, not at all.

Busboys who cleared tables at Chinese buffets across New Jersey have sued claiming their daily wages consisted entirely of tips — minus kickbacks to managers of as much as $20 per shift.

'WE COULDN'T TAKE IT'

One of those workers, Tony Tsai, 30, of Jersey City, said the last straw for the staff at his restaurant in Wayne, N.J., came when the boss threatened to fine every worker $30 for not washing plates thoroughly.

"We couldn't take it anymore," he said.

Other lawsuits have come from workers at nail salons and small retail stores, who say they were never paid overtime.

"There will be more cases in the next few weeks," promised Josephine Lee, a waitress and organizer for a union-backed campaign called "Justice Will Be Served," which has coordinated litigation around New York.

"What we are saying is that there have been rampant abuses, and they need to stop," she said.

Attorney Michael S. Weisberg, who represents the Saigon Grill, said every worker at the company was paid at least minimum wage, which in New York is now $4.60 per hour for tipped food-service workers.

"They make a fortune!" Weisberg said of the delivery men, all of whom were fired after filing their lawsuit, and now picket the restaurant several times a week.

He accused the workers, many of whom are Chinese nationals in the U.S. illegally, of lying about how many hours they worked, and of unfairly turning on a boss who offered jobs without asking too many questions about a worker's immigration status.

"Let them justify one salary that is short!" Weisberg said.

Managers at some of the grocery stores being sued over their treatment of baggers have said the workers weren't employees at all, and were offering their services to customers on their own time.

Still, more scrutiny could be on the way.

This month, New York's state labor commissioner, M. Patricia Smith, announced the creation of a new Bureau of Immigrant Workers' Rights.

The office will help coordinate enforcement efforts, and make sure bilingual investigators are dispatched to inspect potentially unscrupulous employers, said its new chief, Deputy Labor Commissioner Terri Gerstein.

"This administration is strongly dedicated to protecting all workers, regardless of their immigration status, and we will be taking a strong approach to enforcement," she said.

It's not clear that the surge in litigation means there are more violations taking place.

FEWER COMPLAINTS?

The U.S. Labor Department said the number of wage and hours complaints it received last year actually fell for the second straight year, to 26,256, compared with 31,786 in 2004.

Some of the biggest states also reported a decline in wage violation investigations. California opened 38,873 such cases last year, compared with 50,127 in 2002. Texas looked into 15,301 labor violation claims last year, down from 20,138 in 2001.

So why the increase in lawsuits?

Labor attorneys said there has been a proliferation over the past six or seven years in the number of lawyers who specialize in wage and overtime disputes, meaning more cases can be handled without government intervention.

"A few years ago, there were very few people who were toiling in this field," said David Borgen, a labor attorney in Oakland, Calif.

A second explanation could be a growing realization in some immigrant-rich cities that workers can go to court over a pay dispute, regardless of whether they are here legally.

Courts nationwide have, in fact, repeatedly barred employers from trying to kill suits by arguing that their immigrant employees weren't eligible to work in the United States in the first place. In New York, attorney Justin M. Swartz's firm, Outten & Golden LLP, was involved in a $3.2 million settlement with the Gristedes supermarket chain in 2003 over pay for West African delivery workers.

"I think workers, in general, are becoming more and more aware of their rights to be paid properly," he said.