"They're there for one purpose and that's to scare voters," he said. "There is a real concern that some voters have been confused, some voters have been intimidated, and the possibility that they might not show up because of it is a real shame."
Sharp also pointed out the billboards, and brought "Nightline" to one near her home.
"It makes me think back in the '20s and '30s and '40s when everything was segregated," she said, "you know, white people over there, and then black folks and everybody over there."
The billboard company in Cincinnati said the billboards were paid for by an anonymous family fund that wished to remain anonymous, and the billboards have since come down. "Nightline" found no evidence True the Vote was associated with the billboards.
Engelbrecht adamantly denied that True the Vote targets people based on race.
"Teresa Sharp has nothing to worry about because our citizens go into this race-blind, party-blind," she said. "This is literally nothing more than citizens doing what is legally allowed, what anyone can do in an effort to better our overall process and there is nothing more to it than that."
Engelbrecht conceded that the group's software program flags addresses with a high number of registered voters. When asked if the system was biased against people who live in multi-generational homes, she said, "That's the way we segment data just because it is an all-volunteer group that has only limited time."
In a video of an online training session for True the Vote volunteers, obtained by "Nightline" from an activist, an instructor said, "We have to exercise some discretion as we go through this too. You get the wrong person at the keyboard with this tool, if they were doing it for the wrong reasons they could get everyone in trouble. ... All they have to do is find a single judge that is sympathetic to their cause and it shuts us down in every state. So we have to be really careful about who we talk to and what we explain to people about how this thing works."
The instructor said the tool allows volunteers to vet across state lines, processing up to 3,000 voter registrations in 20 hours.
"If you have a friend that you know well, and you want to get him involved, I would just speak in generalities, don't go into real specifics," he said. "Because, like you, we would vet that person. They would sign a non-disclosure."