Transcript for N.D.'s Native Americans say new law blocks many of their population's right to vote

Reporter: Vast and untouched, North Dakota has been the sacred land of several native American tribes for thousands of years. Standing rock is in the center of the United States, and it's probably the heart of this country. Reporter: And most recently, this land, a political flash point. That highly publicized conflict over the Dakota access pipeline, the plight of these native Americans championed by advocates and celebrities like actor Mark Ruffalo and musician Dave Matthews. Everybody knows what they stood up against enormous odds to try and prevent this pipeline from going through. Peacefully, kindly, remarkably. Reporter: Now once again, this community is under the spotlight. Make sure you update your I.D., Patty. Reporter: This time, because of a new I.D. Law some say is intended to make it more difficult for residents here to vote just before the midterm election. As long as I get to the polls and I have to push and shove my way with a piece of paper, I'll get there. Reporter: About 60% of native Americans in North Dakota live on reservations where many residents lack street addresses because the U.S. Postal service does not provide them with residential delivery services, so many native Americans use a P.O. Box to receive their mail. But now in order to vote, you have to have a residential address. That didn't used to be a problem, because there were other ways to prove your residency, like signing an affidavit or having a poll worker vouch for you. But in 2013, the state legislature did away with those back-up options, making it harder to vote, especially for native Americans who live on reservations. We have not been fully colonized to put everything in square streets and boxes. Reporter: Phyllis young is a native American rights activist. We've lived openly and so now we're being forced to create streets and name addresses for our voting rights. Reporter: A legal battle over the new law ensued with the U.S. Supreme court upholding it on October 9th. Do you have your valid I.D. Or no? Reporter: Leaving the native American community scrambling to ensure residents have the proper identification to cast their vote. Do you guys need a ride out to vote or anything? No, we have a car. Reporter: Here at the get out the vote headquarters, a team has been working nonstop for weeks. They've got a valid I.D. For some of them. Some of these -- You got to go back. Okay. And we're going to mobilize our people like we've never mobilized before. It's a critical election nationwide. It's going to make a difference in the congress, in the leadership in this country. Reporter: Critics say it smacks of voter suppression, but secretary of state Alvin says the law was needed, that his office had difficulty verifying voter identities. There was about 3,600 that we couldn't on election day, 97% to 98% of the people that will come to vote will have a state issued I.D. And will be able to vote with no problem. That last 2% to 3%, we're doing everything we can to let their options be known. Reporter: That 2% to 3% affected, most likely native American voters, and because this group tends to vote for Democrats, the new voter I.D. Law matters a lot to senator Heidi Heitkamp. She's the only statewide elected Democrat in a deep red state. She's recently faced backlash for voting against the confirmation of supreme court justice Brett Kavanaugh. I can't get up in the morning and look at the life experience that I've had and say yes to judge Kavanaugh. If it all comes down that decision for some voters, was was it worth it? Yep. I made a judgment based on what I saw and what I heard, and this is a judgment that's not just about the voters today. This is about 30 years of voters in North Dakota, 30 years of people, and to me, I have no regrets. Are you really? Oh my gosh. Reporter: Heitkamp won her seat in 2012 but roughly 3,000 votes so she's keenly aware that every vote counts. The first thing you have to be concerned about is that people who have a right to vote won't be able to vote. Reporter: Secretary of state Jaeger denies the voter I.D. Law was designed to disenfranchise native Americans. Nothing has ever happened in this office to target anybody. Reporter: But just this week, one of the tribes, along with six individuals, took emergency legal action, seeking relief from this requirement that native Americans who live on or near reservations prove a residential address. And across the state, activists are trying to rally local and national support. What we want to do is really inform people about their power as voters here in the state, and the effect of this laurel has created a disparity for American Indian voters. Reporter: Prairie rose Seminole is helping to raise awareness about the new I.D. Requirements. How much power do we have? Let me hear you. Reporter: With a massive get out the vote concert. Headlined by Dave Matthews. So let's vote and continue to fight so that we can try and turn it right. ?????? The people that are being affected by this law in north Dakota are people who have lived on this land for thousands of years. ??? Come out, come out, no use in hiding ??? The state is named after them. And they're being asked to prove, again, that this is their home. It is despicable. And I find it unforgivable. But it's the law. So, we have to deal with it. Reporter: Matthews began working withstanding rock before the Dakota access pipeline conflict, adopting the local elementary school he says now twice in recent years this community has had to lead by example. People brought their disappointment and their hopelessness here to stand with them, which is a weight which lifts you up and also is a burden, and it's remarkable how that so far. Introducing the great white Ruffalo. Reporter: Actor Mark Ruffalo is also putting his star power behind the issue. These people have a reason, plenty of reasons not to vote, and I get that, you know? But I will say this. Whoever wins, you better do right by these people for once. The system has failed us, but we can't change it unless we show up and when we start showing up, nothing can really stop us so that's what gives me hope and I'm going to keep fighting for it. Reporter: For "Nightline," I'm Mary Bruce in North Dakota.

This transcript has been automatically generated and may not be 100% accurate.