(Reuters) - A U.S. appeals court has upheld a lower court ruling requiring Kansas to allow thousands of people who registered to vote at motor vehicle offices to stay on election rolls, despite not showing proof of citizenship as mandated by a state law.

The decision, filed in court papers late on Friday by the 10th U.S. Circuit Court of Appeals, clears the way for these voters to take part in the U.S. election in November.

The decision is not expected to affect the state’s status as a Republican stronghold, but the legal battle over Kansas’ voter identification law has thrust the state into a national debate over voting restrictions.

The National Voter Registration Act allows Americans to register to vote at state motor vehicle offices with no more documentation than they would need to get a driver’s license.

“Under the facts of this case, section five of the NVRA preempts Kansas’ (documentary proof of citizenship) requirement as applied to motor voter applications,” Circuit Judge Jerome Holmes wrote in the court’s decision.

The law is popularly known as the Motor Voter Act.

The legal battle between Kansas officials and the American Civil Liberties Union of Kansas, which brought the lawsuit challenging the application of the state’s voter ID law at motor vehicle offices, involves about 20,000 people who signed up to vote under the Motor Voter Act.

The appeals court affirmed a preliminary injunction granted in May by U.S. District Court Judge Julie Robinson, who ordered Kansas officials to allow those registrants to cast ballots.

Kansas’ secretary of state and the ACLU in an agreement filed in court on Thursday agreed that they could use a standard ballot, rather than be forced to use a provisional one.

Kansas has one of the strictest voter identification statutes in the country, making the state a symbol for mostly Republican Party supporters of such measures who say the rules are meant to prevent voter fraud.

Opponents of the laws, mostly Democrats, say they discriminate against minorities.