An important struggle over home health care is playing out in California, the nation’s most populous state, including nearly five million residents age 65 and older.

Unions and organizations representing the elderly have joined together to push for legislation that would license agencies, certify workers and create a publicly accessible caregiver registry. Home care agencies are pushing back, saying they favor regulation but oppose the measures under consideration. The legislation, Assembly Bill 1217, has already passed the State Assembly and was passed out of the State Senate’s appropriations committee on Friday. It will be up for a vote on the Senate floor next week.

An estimated 1,400 home care agencies and 120,000 paid caregivers would be affected by the proposed legislation, which is essentially an effort to bring consumer protections to an industry that has been likened to the Wild West. “It’s just not right that I can check the license status of an air-conditioning repairman but I can’t do so for someone coming into my home to care for a loved one,” said Assemblywoman Bonnie Lowenthal, a Democrat and the bill’s sponsor.

Currently, a business license is all that is required in California for organizations that offer home care, defined as nonmedical services for the elderly who need help using the bathroom, dressing, bathing and performing other basic tasks.

That leaves older adults and their families without the means to check whether agencies are adequately overseeing their caregiving staff. And elderly people who hire caregivers online or through referral agencies — which maintain lists of caregivers but do not employ them directly — have no easy, reliable way of checking these individuals’ qualifications.

Although agency officials in California insist they follow reputable practices, a study published last year by researchers at Northwestern University found that few agencies perform comprehensive background checks on caregivers or provide reliable training or supervision.

Nationwide, 27 states require home care agencies to be licensed or certified, according to a 2011 report from the Private Duty Homecare Association. A lack of regulatory oversight puts consumers at risk of inadequate care, abuse or neglect, experts warn. Those risks were highlighted in an April 2011 study from the California Senate Office of Oversight and Outcomes highlighting the lack of screening for caregivers.

In one case described in the report, a home care agency placed Daisy Lee Joubert, a convicted felon, in the home of Ileen and Norman Jonas, where she stole an estimated $100,000 in retirement checks and jewelry. Apprehended, Ms. Joubert pleaded guilty to eight counts of embezzlement.

Under the proposed Home Care Services Consumer Protection Act of 2013, California home care agencies would have to obtain a state license by July 1, 2014, or face a fine of up to $900 a day. Agencies would be required to conduct background checks on caregivers, assess their performance annually and supervise their activities in a client’s home every 90 days.

For their part, caregivers would be required to obtain certification after undergoing background checks, a test for tuberculosis and five hours of basic training. Their names and locations would appear on a Web site maintained by the state.

Home care agencies say they have no quibble with licensing and certification requirements. But the agencies think that ensuring the competency of workers should be voluntary and their responsibility, not the state’s, said Dean Chalios, president of the California Association for Health Services at Home, an industry organization.

And home care agencies strongly oppose the creation of a caregiver registry, which would disclose the names of their workers to competitors and union organizers.

“What this is really all about is trying to unionize home care workers in California,” said Kathy Janz, a nurse and executive director of Matched CareGivers, an agency that operates in San Mateo and Santa Clara Counties.

Imposing extra costs on agencies could backfire, making their services unaffordable for families and driving them to gray markets like Craigslist, where no consumer protections exist, warned Assemblywoman Mariko Yamada, a Democrat who earlier this year introduced an alternative bill.

And requiring home care workers to obtain certification could reduce the pool of workers and make it more difficult for the elderly to get services, Kevin Smith, director of operations for the Home Care Association of America, said in a written statement.

Laphonza Butler, president of United Long Term Care Workers, a branch of the Service Employees International Union in California, is a strong supporter of A.B. 1217 and skeptical of the home care industry’s arguments. “If they accept responsibility for training workers and maintaining standards, I wonder why they haven’t done it,” she said.

Gary Passmore, vice president of the Congress of California Seniors, which also supports the legislation, said that “we need to make home care more of a profession,” whether caregivers provide services through agencies or not. With agency costs in California averaging $30 to $35 an hour — versus $15 to $17 an hour for referral agencies and $8 to $12 for individual contractors — middle-class families should have the ability to hire workers who have been vetted by the state directly, he said.

The Direct Care Alliance and PHI (Paraprofessional Healthcare Institute) represent home care workers nationally. Officials at both organizations said in interviews that they supported certification programs and enhanced training for caregivers. The Direct Care Alliance offers a voluntary certification program, but only 807 caregivers have applied. PHI is working with several states to put in place a 77-hour model curriculum for personal care aides, said Steven Edelstein, the organization’s national policy director.

Last year, Gov. Jerry Brown of California vetoed home care legislation similar to A.B. 1217, citing the potential impact on small businesses. But now the state is in better fiscal shape, and it is not clear whether he would veto the bill again if it makes its way through the Assembly.

“Certainly, a goal we’ll continue working toward is to make sure all agencies meet basic standards for providing home care,” Ms. Yamada said.