They work in often low-paid, physically demanding and exploitative conditions, with little to no protection from local labor laws. They are the nannies, housekeepers, elder and disability care workers, doing essential work that others avoid.

The International Labor Organization estimates there are about 100 million domestic workers worldwide.

Of these, some 2.5 million are in the United States. And they're the focus of the first-ever study on wage violations and workplace abuses conducted by labor rights groups and academics.

The National Domestic Workers Alliance, the University of Illinois at Chicago and DataCenter teamed up to publish "Home Economics: The Invisible and Unregulated World of Domestic Work." The study is the result of interviews with more than 2,000 domestic workers in 14 US cities with high concentrations of domestic workers, including San Francisco, Los Angeles, Chicago and Boston. The workers, from 71 countries and speaking nine languages, were asked to describe their experiences.

"A lot of domestic workers don't even get minimum wage," says Claudia Reyes, an organizer with Mujeres Unidas y Activas, an Oakland, California, domestic workers advocacy group that participated in the research. "They have to work overtime and don't get paid for overtime."

Being cheated out of wages is only one manner of abuse some domestic workers endure, she noted, adding that some don't have the right to take a 10-minute break or a break for meals.

No legal recourse

According to the report, nearly half of workers surveyed are paid less than what is needed to support a family, and a quarter of them are paid late. Another 10 percent are not paid at all.

Sylvia Lopez, a 40-year-old native of Mexico, has been a live-in housekeeper in San Francisco for the past four years. She works independently, finding her own jobs. "Sometimes I get called to clean a home and they underpay me or don't pay me at all," she says. "There's no recourse or anyone I can ask to support me to claim my wages."

Lopez, like many other immigrant domestic workers, doesn't have the English skills and knowledge of US law necessary to recover unpaid wages. But she is a legal US resident.

Because many domestic workers are undocumented, they're afraid to speak out about their working conditions for fear of being deported. Lopez says many live-in caregivers have told her that they're often denied rest breaks.

"They never have a moments rest," she says. "The ones who care for children and seniors are woken up in the middle of the night. They always have to be on call and aren't able to get consistent sleeping hours."

Undocumented immigrants often earn far less than the federally mandated minimum wage of $7.25 (5.47 euros) per hour. In an effort to address these issues, domestic worker rights bills are cropping up in state legislatures around the US.

In 2010, for instance, New York became the first state to pass a domestic worker rights bill to grant domestic wage and hour and workplace protections. Massachusetts and Illinois are debating similar bills.

California veto

But the situation in other states looks less bright. Although a bill that would have provided minimum wage guarantees, overtime pay and meal breaks, among other rights, made it all the way to California Governor Jerry Brown's desk in October, Brown vetoed it. In a statement, he cited several concerns, including the ability of low income seniors and disabled people to pay caregivers higher wages.

"We had a struggle, especially in the Senate, but they did it and we were so pleased and then we had the rug pulled out from under us by Jerry Brown," says California State Assembly member Tom Ammiano, who co-authored the bill.

Domestic worker advocates say they worked with disability rights groups to find a compromise.

"The disability rights organization had removed their opposition to our bill by the time it reached his desk and were actually indignant that their community was used in the veto message as [Brown's] reason," says National Domestic Worker Alliance Field Director Jill Shenker.

Ammiano hasn't given up his effort to make the so-called "Trust Act" law.

"We're coming back full tilt and hopefully within the next two years we will get this bill passed," he says.

In the 1930s, domestic and agricultural workers were excluded from the Federal Fair Labor Standards Act, which established a minimum wage, the right to join unions and the right to overtime pay, among other gains. Excluding farm and domestic workers was a compromise to appease southern lawmakers whose economies were more dependent on those types of jobs, which at the time were mainly carried out by black workers.

Domestic worker advocates say it's time for protections to be extended to all categories of workers.

"Domestic workers are doing critical work in our country, making it possible for families to balance their work and home lives," says Shenker.

In 2011, the International Labor Organization, an arm of the United Nations, passed a Domestic Worker Rights convention. The treaty set guidelines for signatory nations to bring domestic workers under their local labor rights laws. Among its recommendations: guaranteed overtime pay, mandatory rest breaks and minimum wages to domestic workers.

So far, only the Philippines, Uruguay and Mauritania have ratified the treaty. The US has declined, arguing that such issues are best settled at the individual state level.

For many US-based domestic workers, that means continued economic struggles. Still, together with labor rights activists, they hope someday to win their rights in state legislatures across the nation.