Calfornia sends voter registration forms to 4 million enrollees as part of legal settlement with voting rights groups. (Jonathan Alcorn/Reuters)

California officials have started sending voter registration forms to 4 million people who shopped on the state’s new online health insurance marketplace, as part of a legal settlement with voting rights groups that are urging states to make it easier for people to sign up to vote as they enroll in coverage.

The groups, including the American Civil Liberties Union, had threatened legal action against California, arguing that it did not comply with the 1993 National Voter Registration Act. The law requires that people in 44 states and the District of Columbia be given the chance to register to vote when they apply for public benefits, such as Medicaid and food stamps.

The groups argue that the new state and federal health insurance marketplaces set up under the 2010 health-care law offer public benefits and therefore must give people an opportunity to register to vote.

The federal marketplace, which serves 36 states, and most of the marketplaces run by the states do offer some people a way to register. But the groups say the process is not easy enough to comply with the law, and they are pressing their case in more than a dozen other states.

“Ensuring that all eligible Americans are registered to vote is key to ensuring a robust democracy,” Lisa Danetz, legal director of Demos, a left-leaning think tank, said in a statement. “If other states follow, millions more Americans will have the opportunity to join the voting rolls.”

ACA enrollment numbers, state-by-state

Many of those who would benefit from the health-care law are low-income, and low-income people are more likely to register as independents or Democrats than as Republicans. Still, the effort to expand access to voter registration through the marketplaces has encountered little political pushback.

It is unknown how many of those eligible to obtain insurance through the exchanges are registered to vote, although surveys suggest that low-income people participate less in elections compared with higher-income people.

California’s marketplace, Covered California, had provided a voter registration link on its homepage. But some applicants bypass the homepage, said Sarah Brannon, a director at the nonprofit Project Vote. And there was no option for people using a paper application, she said.

California officials said they have been working to make it easier for people to register to vote while shopping for insurance. But initially, they were focused on the marketplace’s core function: signing people up for health insurance.

“We will be in full compliance through all application channels by the first day of open enrollment in fall 2014,” said Anne Gonzales, a spokeswoman for Covered California.