A leading climate sceptic patronised by the oil billionaire Koch brothers faced a potential investigation today on charges that he misled Congress on the extent of his funding from the oil industry.

Patrick Michaels, a senior fellow in environmental studies at the Cato Institute, a thinktank founded by Charles and David Koch to promote their libertarian, anti-government views, appeared before the house energy and commerce committee in February 2009.

At the time, the committee was headed by the California Democrat Henry Waxman and Michaels was the only one in the line-up of witnesses to cast doubt on global warming, testifying that mainstream science had exaggerated the threat posed by climate change.

Now, Waxman writes in a letter to the incoming committee chair, Fred Upton, it appears as if Michaels may have misled the committee. In 2009, Michaels said 3% of his $4.2m in financial support came from the oil and gas industry. But in an appearance on CNN in August last year, and in subsequent interviews, Michaels suggested that figure was 40%.

"Michaels may have provided misleading information about the sources of his funding and his ties to industries opposed to regulation of emissions responsible for climate change," Waxman writes in the letter, released on Monday.

Waxman urged Upton to call on Michaels to clarify the sources of his funding, and to give a complete account of his funding sources to the committee.

The request for an investigation is a turn on the Republicans, who have set out a long list of potential targets for scrutiny since their takeover of the house, starting with the Environmental Protection Agency.

Michaels has also received direct funding from the Koch brothers. From their base in Wichita, Kansas, the Kochs control the largest privately held oil company in the US. They gained notoriety during the mid-term elections for bankrolling a leading, conservative Tea Party organisation, Americans for Prosperity.

But the Kochs have for years been funnelling money to organisations which oppose government regulations and deny the existence of climate change.