Lieutenant governor candidate Geoff Duncan is challenging his GOP runoff opponent, state Sen. David Shafer, to release his taxes and further specify how he became a multimillionaire.

Not only is Duncan calling on Shafer to release tax returns from the 16 years he has served in the state Senate, but the Cumming Republican also is encouraging anyone with information about how the senator earns a living to submit an anonymous tip on a newly launched website.

Duncan, a former state representative, on Wednesday released his tax returns from the years he served in the state House.

“Unlike my opponent, I am more than willing to be transparent about how I earned a living — particularly during the short time I represented the people Forsyth County in the state Legislature,” Duncan said.

Shafer filed a 16-page financial disclosure in March, listing a net worth of about $5.6 million in 2017. He has filed a disclosure each year in office.

Shafer said he has invested in several businesses, including some that sell liability insurance, and a warehousing business he purchased from his father-in-law.

“Geoff Duncan will do or say anything, no matter how desperate, dishonest or self-demeaning,” said Bryan Piligra, a campaign spokesman for Shafer. “Now he is borrowing stunts from Hillary Clinton’s playbook.”

On the website, www.ShaferWhistleblowers.com, Duncan asks for anyone to submit anonymous tips.

“If the decades’ worth of rumors are not true, then I expect the website to be very quiet,” Duncan said. “My guess is that we’re going to be able to connect some very unfortunate dots that will help both us and the rest of the folks in Georgia better understand who David Shafer really is.”

Lt. Gov. Casey Cagle and Secretary of State Brian Kemp emerged as the top finalists in Tuesday's election.

During a press conference Wednesday, Duncan offered no evidence of corruption.

Duncan is seeking traction ahead of the July 24 runoff after Shafer nearly won May’s three-man GOP primary outright.

Shafer got 49 percent of the vote, while Duncan got 26.6 percent. A third candidate, former state Sen. Rick Jeffares, garnered 24.4 percent. Jeffares has since endorsed Shafer.

Shafer’s source of income has been targeted by his opponents throughout the primary.

Both Duncan and Jeffares asked Shafer during a televised Georgia Public Broadcasting debate last month to explain how he makes his money.

Duncan said he and his team will weigh the responses that come into the website and determine how true they are.

“We will talk about something when it’s 100 percent true,” he said. “If something smells criminal and corrupt, we’ll notify the appropriate officials to investigate. If something comes in and it looks frivolous, we’re not going to run forward with it.”

According to Duncan’s financial report filed in March, he had a net worth of nearly $1.8 million in 2017.

Duncan’s tax returns show that his income fluctuated from 2013 to 2016.

In 2013, he and his wife reported about $91,000 in earned wages, interest and real estate. His reported income in 2014 was about $198,000. Duncan reported an income of about $85,000 in 2015. In 2016, Duncan reported earning about $255,000.

Duncan owns a small marketing business and consults with health and construction companies, according to his financial statement. His wife is a nutritional health coach.

Shafer spokesman Piligra said: “Duncan served as the front man for a company that was set up to profit from Obamacare regulations.‎ He is the one who is feeding from the swamp.

The spokesman added, “His own tax returns raise unsettling questions about how he has earned his living, afforded his home and accumulated his claimed wealth.”