Oregon state Rep. Knute Buehler is taking a tough new stand against one of his rivals in the Republican primary race for governor.

Buehler has launched a radio advertisement criticizing Bend businessman Sam Carpenter for frequently failing to pay his state, federal and local taxes on time. Records show Carpenter was hit with six federal and state tax liens in the 1990s and his business had 15 tax liens.

THANKS TO OUR SPONSOR: Become a Sponsor

“If Sam Carpenter can’t pay his own taxes,” says the radio ad, “why should we trust him with our tax dollars?”

Carpenter scoffed at the attack, saying he eventually paid all of the tax liens. He said they mostly occurred in the 1990s when his telephone answering business was struggling and he went through a divorce.

"I’ve never not paid anyone back,” he said. “I never declared bankruptcy.”

Buehler has been regarded as the front-runner in the primary race. He’s the only one in the 10-candidate field who can afford a major advertising campaign and he has several key business and political endorsements.

Related: Buehler Looks To November As Other Republicans Question His Conservatism

THANKS TO OUR SPONSOR: Become a Sponsor

But Buehler has come under fire from Carpenter and some other conservatives for supporting abortion rights and for recently supporting a gun control bill. They also complain that Buehler has often criticized President Donald Trump.

Carpenter, who emphasizes his strong support for Trump, has built a following in the race. Retired Naval aviator Greg Wooldridge has the backing of Oregon Right to Life and also has become a factor in the contest.

The Buehler campaign did not discuss the tax issues mentioned in the mailer and radio ad. But it did release a statement from Buehler saying he was joining the Oregon Tea Party and a “chorus of voices” condemning Carpenter “for his false attacks and repeated lies.”

The Tea Party put an unsigned statement on Facebook saying that “the Carpenter campaign is obsessed with attacking anyone who doesn’t support their candidate with whatever despicable tactics they can drag up.”

The Buehler campaign’s new ads may indicate that he and his aides are concerned about the level of Carpenter’s support — or that at a minimum they want to discredit him as a voice for Republican conservatives.

Carpenter said he thinks the ads show that he’s got a shot at winning the May 15 primary. “When you’re taking incoming flack,” he said, “you’re over the target.”

Tax records show that five federal tax liens and one state tax lien were filed against Carpenter between 1990 and 1996. The amounts totaled more than $40,000.

His business, Colejenn Inc., was hit with 15 federal, state and county tax liens between 1990 and 2012 totaling more than $90,000. The largest was a 2004 federal tax lien of $70,607. Records show it was paid two years later.

Carpenter acknowledged in his 2014 book, “Work the System,” that his business was in shambles in the 1990s. He had high employee turnover, trouble making payroll and was often forced to cover overnight shifts on his own.

He was divorced for his fourth time. The 68-year-old Carpenter said Wednesday that, “I had a nightmare of a life until I was 50.”