California Gov. Jerry Brown on Sunday signed into law a bill holding the state's employers legally responsible for wage and safety violations committed by their subcontractors and temp agencies.

With the new law, California will have some of the country's farthest-reaching protections for temporary workers, among the fastest growing and most vulnerable segments of the workforce.

The legislation was introduced this year after a series of stories by ProPublica documented abuses and dangers faced by legions of blue-collar temp workers, California labor officials said. It was overwhelmingly supported by lawmakers.

The growing reliance on temp work in recent years has led to complaints from workers nationwide who say they've been cheated on wages or ordered to work in unsafe situations. But their complaints had little impact as temp agencies blamed the companies that hired them and those companies, in turn, faulted the agencies.

The new law is designed to protect low-wage workers, including hotel maids, factory assemblers, warehouse workers, farm laborers, food processors and janitors, who often work for years at the same company, but are paid less and denied the benefits of full-time employees because they are officially employed by a labor contractor.

ProPublica's investigation showed workers arriving at temp agency dispatch halls at 4 a.m., then waiting for hours to be packed onto overcrowded vans and shuttled to assemble products and unload trucks for some of the biggest-name companies in America. The workers regularly faced mandatory fees that pushed their pay below the minimum wage.

Federal and state safety investigations have found case after case of untrained temp workers pulled into food grinders and conveyor belts, asphyxiated while cleaning the inside of chemical tanks or  overcome by heat stroke after a long day on a garbage route. A ProPublica analysis of millions of workers' comp claims found that in California, temp workers were about 50 percent more likely to get injured on the job than their regular counterparts.

Despite these problems, the United States has lagged behind the rest of the developed world in adopting laws to protect the growing number of temps. Faced with similar abuses, countries from Argentina to Korea have limited the length of temp assignments, guaranteed equal pay for equal work, or restricted companies from hiring temps for hazardous jobs.

In most states in the U.S., a worker would have to prove in court that a company had sufficient control over the workplace to hold that company accountable. For example, Andro Tolentino, a temporary housekeeper at the Westin Crown Center in Kansas City, Mo., has fought for more than six years after his employer didn't pay him for cleaning 122 rooms in April 2008. His temp agency, Giant Labor Services, promised to pay him $3.50 per room, but then deducted fees that wiped out his wages.

Giant was subsequently federally indicted on labor violations. Westin and its parent company Starwood Hotels & Resorts argued that they weren't responsible because Tolentino was Giant's responsibility, not theirs. The Missouri Supreme Court disagreed, ruling last month that Starwood could be held liable for the unpaid wages.

Under the new California law, sponsored by Assemblyman Roger Hernandez, D-West Covina, companies could face fines if the temp agencies they use or their subcontractors fail to pay employee wages or provide workers' compensation insurance. The law gives companies a grace period to get temp agencies to comply.

Teamsters national president Jim Hoffa said in a statement that Brown had closed a loophole that allowed corporations to take advantage of workers.

"Today marks a new era for worker protection in California," he said. "No longer can employers hide behind unscrupulous labor contractors. Workers, no matter if they are temporary or permanent, can hold companies who profit from their labor accountable for violations in the workplace."

The California Chamber of Commerce had labeled the bill a "job killer" and said it would scare away business by punishing innocent companies for violations they were unaware of and had no authority to prevent.

The law exempts homeowners, highly-paid tech workers, trucking and cable companies, small businesses and companies that don't employ more than five temp workers at a time. It takes effect on Jan. 1.