States across the country are violating part of the federal "motor voter" law requiring voter registration help for low-income residents, according to a coalition of advocacy groups trying to force change through the courts.

The groups filed lawsuits in Indiana and New Mexico on Thursday on the heels of a successful settlement in Missouri. They say the problem is not isolated in those few states but widespread across the nation, and they are trying to help other states follow the law without litigation.

They complain that the Bush administration didn't do more to enforce the law but say the Obama Justice Department has assured them it will.

"We will aggressively seek compliance -- through litigation if necessary -- to broaden the ability of Americans to participate in our democracy," said Justice Department spokesman Alejandro Miyar.

However, the Obama administration has yet to take legal action, so the advocacy groups are suing states themselves.

Brenda Wright, director of the Democracy Program at the nonprofit group Demos, one of the groups behind the lawsuits, said 2.6 million people were registered through public assistance offices in 1995-1996, the first two years the law was in effect. But registration has dropped precipitously throughout the nation since then, by 90 percent or more in some states, she said.

"If the law is being ignored, you have an important segment of the community that really needs a voice in politics being left out," Wright said. She said 2 million to 3 million more low-income people could be registered each year if all states followed the law.

The suits say that the states are violating the 1993 National Voter Registration Act, nicknamed "motor voter" because it requires states to offer voter registration when residents apply for a driver's license or state ID. To reach low-income citizens less likely to own vehicles, the law also requires that voter registration cards be distributed along with applications for public assistance like food stamps and Medicaid.

The coalition of advocacy groups, which also includes the Association of Community Organizations for Reform Now, Project Vote and the Lawyers' Committee for Civil Rights Under Law, says most states have programs for driver's license registration, but many ignore the public assistance requirement.

For example, Project Vote reported that none of 21 people interviewed as they left Indiana public assistance offices last year had been given a voter registration application despite the law's requirement to do so. Of seven Family and Social Services Administration offices that Project Vote investigated, six had no voter registration forms available even upon request. That included offices in such economically depressed Indiana cities as Gary, East Chicago, and Indianapolis.

The result was that, even as more people signed up for food stamps in Indiana, voter registration applications received from public assistance offices plunged by 97 percent -- from 3,494 in 1996 to 105 in 2008, the lawsuit said.

There's been a 91 percent drop in voter registration from New Mexico's public assistance offices during the same period, the groups say.

The New Mexico Human Services Department said in a statement that it was "shocked" that the groups would file a lawsuit after officials have been cooperating with them for a year and a half to ensure voters were being registered in their offices. Indiana officials did not respond to a request for comment.

Last year, a federal judge ordered the Missouri Department of Social Services to comply with the law after the groups sued. As part of a settlement two weeks ago, the department will provide monthly reports on its efforts to comply with the law and agreed to reimburse ACORN $450,000 in legal costs.

Wright said 112,000 people have registered to vote though Missouri public assistance offices in the last nine months since the judge's order went into effect, compared to 15,000 in the previous two years.

Wright said the advocacy groups' coalition, called the National Voter Registration Act Implementation Project, have been trying for several years to encourage states to come back into compliance. She said the project has succeeded without going to court in some states, like North Carolina and Virginia, which worked to solve the problem after it was brought to the attention of state officials.

Demos says Virginia has seen a fivefold increase in monthly registration applications. And in North Carolina, over 80,000 low-income citizens applied for voter registration at public assistance agencies in the two years since the coalition worked with state officials, compared to only 11,600 in the previous two years.