California Attorney General Xavier Becerra filed his 50th lawsuit against the Trump administration on Monday, challenging a ban on deduction of union dues from the paychecks of hundreds of thousands of workers providing in-home care for low-income elderly and disabled people.

Medi-Cal provides 594,000 Californians with assistance — in bathing, cleaning, meals and other essentials that allow them to stay in their homes — by funding more than 500,000 workers, most of them women, Becerra’s office said. More than half the workers belong to unions and since the early 1990s have had their dues, and in some cases payment for union-sponsored health benefits, automatically deducted from their paychecks. Those paychecks are funded by the state and federal governments.

Last week, President Trump’s Department of Health and Human Services published a rule that prohibited union payroll deductions, contending they violated a 1972 law barring the “assignment” of federal health care payments to anyone but the care provider. Becerra’s lawsuit in San Francisco federal court, joined by the states of Connecticut, Massachusetts, Oregon and Washington, said the rule was legally unfounded and would harm the workers and the people they care for.

“This rule jeopardizes the health of vulnerable Californians who are currently able to live at home thanks to Medi-Cal’s (in-home care) program,” Becerra said in a statement.

April Verrett, president of Service Employees International Union Local 2015, which represents many of the workers, commended Becerra for “taking the lead on this action against this hateful federal rule change targeting home care providers.”

The federal agency declined to comment.

Becerra, a former Democratic congressman, was appointed by then-Gov Jerry Brown to succeed Kamala Harris as attorney general in January 2017 and elected to a four-year term last November. He has regularly sued the Trump administration over its policies on issues such as immigration, the environment and health care, most of them substantial changes in previous federal practices.

One suit challenged Trump’s ban on U.S. travel from a group of mostly Muslim countries, an edict that the Supreme Court upheld in its third version last year. Becerra has also joined other states in challenging the president’s declaration of an immigration emergency to divert billions in funding for construction of a border wall, a suit that is scheduled to be heard Friday by a federal judge in Oakland.

Overall, Becerra’s office said, he has won 34 of the 49 suits filed before Monday. But his winning percentage may decline as some of the cases — including rulings against the addition of a citizenship question to the 2020 census and a ban on transgender service in the U.S. military — receive final verdicts from the Supreme Court and its conservative majority.

In defense of the new rule on home care workers, Health and Human Services representatives said the workers could send dues payments to the unions on their own. The states’ lawsuit said that would be more cumbersome and highly unlikely, and that the administration’s real goal was to weaken unions.

Quoting a letter from the UC Berkeley Center for Labor Research and Education, the suit said making it harder for employees to pay unions “could result in lower worker wages, higher worker turnover, greater worker shortages, poorer quality of care, and an increase in the overall cost of long-term care.”

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com Twitter: @BobEgelko