The hourlong debate will focus on "economic freedom," said the conservative organization's state director, Evelyn Everton. The questions will range from taxes and regulations to health care and energy production.
"This is an opportunity to provide a forum so that voters in the district can get a really good idea of where these candidates stand," she said.
Democrat Kathie Allen — who's raised nearly $700,000 in donations — did not respond to an invitation to join the event, Everton said. Allen and her campaign staff, though, said they were not aware that she'd been asked to participate.
Still, Allen said she plans to focus her energy on the Nov. 7 general election, which she's already qualified for.
"We've decided to debate whoever comes out as the Republican nominee," Allen said.
Though Tuesday's event is free, attendees are asked to register online. About 250 people have already claimed tickets and the auditorium holds 600. Doors open at 6:45 p.m. T-shirts and pins promoting a candidate are prohibited.
The July 28 debate, hosted by The Salt Lake Tribune and the Hinckley Institute of Politics, is slated for 7 p.m. at the Utah County Convention Center, 220 W. Center St., Provo. The GOP candidates will answer questions and offer rebuttals on public lands, education and the international role of the United States (including interactions with Russia).
"We hope this debate provides a forum for candidates to explain their priorities and for the public to ask questions and get them on the record," said Tribune editor Jennifer Napier-Pearce.
Attendees, to be capped at 500, can submit questions for the hourlong event using #UT3debate on Twitter.
Hinckley Institute director Jason Perry said voters should pay particular attention to the upcoming debates, given the abbreviated timeline of the special election.
"Oftentimes we have a chance to really understand and vet candidates for a significant period of time before the election," he said. "But because of the compressed schedule, debates like this are going to be the key times for Utahns in the 3rd District to figure out who they're voting for."