Dave Matthews and Mark Ruffalo to host free concert in North Dakota to encourage Native American voters

Actor Mark Ruffalo and musician Dave Matthews are the latest celebrities to shed light on a strict voter ID law in North Dakota that disproportionately affects thousands of Native Americans in the state.

Ruffalo and Matthews announced a free concert in Cannon Ball, North Dakota, one of the largest communities on the Standing Rock reservation in Sioux County, for a Get Out the Vote event on Saturday that's intended to encourage native voters to get new IDs that meet voting requirements.

Billy Ray Cyrus, the singer and father of Miley Cyrus, also recently spoke out on the issue, tweeting at ABC News after reading coverage of the story.

Ruffalo and Matthews both protested the Dakota Access Pipeline in Standing Rock back in 2016 and recently joined the Stand-n-Vote campaign to encourage Native American voters to head to the polls. The free concert will also feature Native American performers like Auntie Beachress, a comedian, Lakota Thunder and the Dancers of Northern Plains and Prolific the Rapper.

The event is in reaction to an action by the Supreme Court last week, which allowed the state to go forward with a voter ID law requiring all North Dakotans to provide IDs with a residential address at polling places. Many residents on reservations, however, don't have or use residential addresses because they live in such rural areas and instead rely on P.O. boxes for mail.

The state maintains that the law is intended to combat voter fraud, not disenfranchise voters.

But according to studies commissioned by Native American rights groups who sued North Dakota over the new law, roughly 35 percent of that population doesn't have an acceptable ID with a residential address. In order to vote on Election Day, Native Americans must get a new state- or tribal-issued ID with updated information.

"The intent of the event is to take a united stand against rampant voter suppression, not only in North Dakota, but nationally. The event is also intended help Get Out the Vote in the upcoming November 6 midterm elections, and to encourage native voters to get new tribal IDs so that they can vote in this election," said a press release for the event.

The question of whether Native American votes will be counted is an especially relevant one in the upcoming midterms because, in less than two weeks, Native Americans across North Dakota will be among the nation’s most important groups in an election likely to help determine Senate control.

North Dakota’s voters are the most powerful in the country, according to FiveThirtyEight’s voter power index, and significant attention has been paid to the Native American voting bloc because of their overwhelming support for Democratic Sen. Heidi Heitkamp when she was first elected by a narrow margin in 2012.

ABC News' Roey Hadar contributed reporting.