The United Farm Workers union sued California's occupational health and safety agency on Thursday, accusing it of doing too little to prevent farm laborers' deaths from heat illness.

A tomato picker heads for the truck as he works in a field near Stocktonon on Wednesday, July 30. A recent report found that between 1992 and 2006, U.S. crop workers died from heat illness at a rate 20 times greater than all other workers. (Bryan Patrick/ Sacramento Bee) The lawsuit, filed in state Superior Court in Los Angeles, says 11 farm workers have died from heat illness since California adopted regulations in 2005 aimed at stopping such deaths. It says that the regulations are too weak and that the safety agency has too few investigators and inspects too few farms, where laborers often work in heat exceeding 100 degrees.

Six farm workers died from heat illness last year, according to the lawsuit. State officials say three did. None have died this year, but several were taken to the hospital, lawyers for the union said.

Last year, the state found that more than 35 percent of the growers it had investigated violated the regulations.

Officials with the California Division of Occupational Safety and Health said they have increased efforts to prevent heat-related illnesses.

They said that since a heat wave began on July 11, the agency had conducted 167 inspections of outdoor workplaces and found more than 200 violations.

"We have done more enforcement this year than we have over all in past years," said Dean Fryer, a spokesman for the Department of Industrial Relations, who said the enforcement has resulted in more compliance. The agency, he said, has taught more than 5,000 growers and farm labor contractors about the requirements of the heat regulations.

State inspectors ordered 10 employers to suspend operation because of violations, including one grower who had less than one gallon of water for 15 employees working in 116-degree heat.

The lawsuit maintains that the regulations wrongly place the burden on the workers to say they need a break and some shade when they start to suffer from the heat. By then, the lawsuit says, some workers might be in grave danger.

"It's extremely difficult for workers to step forward, especially because they often work at piece rates, and they're not paid when they take a break," said Catherine Lhamon, assistant legal director for the American Civil Liberties Union of Southern California, which helped file the case.

The lawsuit says California should require that growers set triggers at various temperatures at which point growers would have to give workers a rest in the shade. It says that the regulations require growers to give just a five-minute break to workers who complain about the heat.