BISMARCK, N.D. (AP) — The Spirit Lake Sioux tribe on Tuesday sued the state of North Dakota over its voting identification requirements, part of a larger effort to ensure American Indians can vote in next week’s election in the wake of a U.S. Supreme Court ruling in a similar lawsuit filed by another tribe.

To cast a ballot, voters in North Dakota need identification with a provable street address — something that’s hard to come by on reservations. The state maintains everyone has a street address via the statewide 911 system, but the lawsuit filed by the Native American Rights Fund, the Campaign Legal Center and two law firms argues the system is “incomplete, contradictory and prone to error on reservations.”

“State policies should be designed to make it easier for all citizens to vote, but North Dakota’s voter ID law disenfranchises Native Americans living on reservations,” said Danielle Lang, senior attorney with the Campaign Legal Center.

The lawsuit filed in U.S. District Court seeks to have the street address requirement ruled unconstitutional.

“We have a choice between a democracy that includes all eligible voters and a system that excludes people based on their circumstances or backgrounds,” Lang said. “Unless the court steps in, eligible Native American voters including our clients may be denied the right to vote next week due to the state’s deeply flawed system of assigning and verifying voters’ residential addresses.”

Secretary of State Al Jaeger said the state does not comment on pending litigation.

The Turtle Mountain Band of Chippewa sued over the voter ID requirements in 2016. A U.S. Supreme Court ruling in that case earlier this month allowed the state to continue requiring street addresses, as opposed to other addresses such as post office boxes. However, Justice Ruth Bader Ginsburg said in a dissent that “the risk of voter confusion appears severe here.”

North Dakota’s four large American Indian tribes have been scrambling since the Supreme Court decision to make sure their members can vote in the election, which includes a race that could help determine control of the U.S. Senate. Republican U.S. Rep. Kevin Cramer is challenging Democratic incumbent Sen. Heidi Heitkamp — who narrowly won her seat in 2012 with the help of the American Indian vote.

The state’s voter ID laws were tightened just a few months later, but the Republican-controlled Legislature maintains the changes were not due to Heitkamp’s win. Jaeger has said the changes were aimed at guarding against voter fraud.

The four tribes in recent days have been issuing free IDs with residential street addresses to their members, but the Spirit Lake lawsuit argues that the 911 addressing system on reservations is “characterized by disarray, errors, confusion, and missing or conflicting addresses.” It cites several examples of what it says are tribal members who have experienced problems, including one man who used the residential street address listed on his state-issued ID on an absentee ballot application and had it denied due to an “invalid” address.

The skirmish over voter access isn’t limited to North Dakota. Voters in at least eight states will face more stringent laws than they did in the last federal election, according to the nonpartisan Brennan Center for Justice.