Two former Oregon governors on Monday called on Republican nominee Knute Buehler to release his full tax returns.

Buehler and his wife released the first several pages of their federal tax returns from 2015 to 2017 earlier this year, while Democratic Gov. Kate Brown and her husband released their full returns for the same time period.

In a news conference in Southeast Portland, former Govs. Ted Kulongoski and Barbara Roberts said Buehler should release his full tax returns so that voters know whether the Bend legislator and orthopedic surgeon is "paying his fair share" of taxes and has a personal interest in public policies he would pursue if elected governor. Both Kulongoski and Roberts are Democrats who support Brown's re-election bid.

"It's fair for the citizens to ask: 'If you want to spend my tax money, I want to know if you're paying your fair share,'" Kulongoski said. "That's the issue. Tell the public what you're doing."

As The Oregonian/OregonLive reported in July, the Buehlers' effective federal tax rate is around 25 percent on income that reached $1 million one year, while Brown's household income was approximately $190,000 and her effective tax rate was roughly 15 percent.

"I know people in that tax category who are paying higher rates than that," Roberts said of the Buehler's effective tax rate.

Monica Wroblewski, a Buehler spokeswoman, said the couple voluntarily released three years of tax returns and already has disclosed financial investments, businesses, property and sources of income during the three years, 2015 to 2018, Buehler has been in elected office.

They have "gone beyond what is required by law to be transparent about their personal finances," she said in a news release. "Releasing additional financial details of their businesses (Schedule E) is an unreasonable expectation that invades the privacy of citizens, who are business partners ... and have no role in public life."

Brown's campaign has highlighted the Buehlers' purchase a decade ago of $100,000 worth of business energy tax credits, which the East Oregonian reported on Friday. Christian Gaston, a spokesman for Brown's re-election campaign, suggested it was hypocritical of Buehler to repeatedly criticize the scandal-ridden program, including in an editorial and in a speech opposing a different state program — the low-carbon fuel mandate — on the House floor without disclosing that he benefitted from it.

Oregon ended the business energy tax credit, which allowed thousands of businesses and wealthy individuals to reduce their tax bills and could have cost the state as much as $1 billion in tax revenue, in 2014. Buehler took legislative office in 2015.

The legislator called out Brown for failing to "investigate or fix the tax credit program while it was wasting millions under her nose" as secretary of state.

"The fact that I legally purchased tax credits as a private citizen years before the program was revealed to be a wasteful mess by investigative journalists and not Kate Brown, does not disqualify me from being critical of the program as a lawmaker," Buehler said in a prepared statement.

The business energy tax credit was a longstanding program, and the problems that led to its demise — including a gross underestimate of how much tax revenue Oregon was giving up — occurred while Kulongoski and former Gov. John Kitzhaber were in office. For example, an investigation by The Oregonian/OregonLive found that Kulongoski's administration pressured Energy Department employees to lowball the potential cost in order to gain support in the Legislature.

"There's nothing wrong with tax avoidance," Kulongoski said on Monday. "So you shouldn't be ashamed if you're taking advantage of it."

Former Gov. Ted Kulongoski spoke at a press conference Monday calling for Rep. Knute Buehler to release the rest of his tax returns.

The business energy tax credit was back in the news last week, when the state took the rare step of clawing back $13 million worth of tax credits that were issued based on inflated costs. The Oregon Department of Justice and FBI originally launched investigations of the university solar projects in 2015, after The Oregonian/OregonLive reported on inflated costs for university solar projects that were a priority for Kitzhaber.

A 2016 audit by a Portland financial crimes consultant uncovered sufficient "circumstantial evidence of suspicious behavior" in 79 business energy tax credits to warrant referral to the Oregon Department of Justice. It was the first time the state, with its audits division under Brown's direction as secretary of state from 2009 through early 2015, had commissioned an audit of the credits. The DOJ has yet to announce it is investigating any of those tax credits.

-- Hillary Borrud

503-294-4034; @hborrud