Twenty years ago, Congress passed a controversial law requiring states to allow people to register to vote when they applied for driver’s licenses or social services. Now, that same law is bringing voter registration to the health-insurance marketplaces, a move that some anticipate will result in legal fights and inspire even more partisan debate over the new health-care law.

According to the 1993 National Voter Registration Act, motor-vehicle departments and places that provide public assistance, such as food stamps or Medicaid, or services for people with disabilities, must also offer voter registration. But states are divided over whether the law applies to the insurance marketplaces.

Hawaii concluded that its exchange was not responsible for registering new voters, while several other states, including Connecticut, Vermont and California, have designated theirs as mandated voter-registration agencies. Colorado determined that the exchange is not a state agency but decided to put a voter-registration link on its website anyway.

The federal government, which is running exchanges for 36 states, determined that voter registration must be offered to consumers because the Centers for Medicare & Medicaid Services rules on Medicaid eligibility. Both the paper and the online applications include a line that says, “If you want to register to vote, you can complete a voter registration form at usa.gov.”