WASHINGTON: Escalating a political fight over global warming, a Republican House chairman issued subpoenas Wednesday to two Democratic state attorneys general, seeking records about their investigation into whether Exxon Mobil misled investors about man-made climate change.

Texas Representative Lamar Smith, chairman of the House Science Committee, is pursuing records from New York Attorney General Eric Schneiderman and Massachusetts Attorney General Maura Healey along with nine environmental, scientific and philanthropic organizations. Smith insisted he acted only after they refused for months to give the panel information lawmakers had requested on the Exxon Mobil case.

Smith, who is among a large group of congressional Republicans who reject mainstream climate science, said Schneiderman and Healey were pursuing "a political agenda" on behalf of environmental groups that are fighting Exxon over decades-old research related to climate change.

The groups accuse Exxon of hiding early findings showing a link between global warming and the burning of fossil fuels such as oil and gas. Exxon denies that it suppressed findings from its own research that dates back more than 30 years.

Smith and other Republicans portrayed the issue as a matter of free speech, charging that Schneiderman, Healey and their allies were trying to intimidate scientists and others who question man-made climate change.

"The actions by the attorneys general amount to a form of extortion," Smith said at a news conference at the Capitol. The two officials and their allies want an out-of-court settlement with Exxon and other companies "so they can obtain funds for their own purposes," Smith said.

A spokesman for Schneiderman said the science panel had no legal authority to issue subpoenas to a "duly elected, constitutional officer of a separate sovereign government."

Spokesman Eric Soufer accused "a small group of radical Republican House members" of "trying to block a serious law enforcement investigation into potential fraud at Exxon. Chairman Smith and his allies have zero credibility on this issue, and are either unwilling or unable to grasp that the singular purpose of these investigations is to determine whether Exxon committed serious violations of state securities fraud, business fraud and consumer fraud laws."

Exxon has called the state investigations an effort to silence the company in the public debate about climate change.

Two environmental groups that were issued subpoenas said Smith and other Republicans were acting on behalf of Exxon and other oil companies that have contributed thousands of dollars to their campaigns.

"Rep. Smith's acceptance of large donations from Big Oil and Gas provides explanation into his history of baseless attacks against climatescience," the groups 350.org and Greenpeace USA said in a statement. Since 2008, Smith has received a total of $675,597 from the fossil fuel industry, $19,500 which came directly from Exxon Mobil, the groups said.

Rep. Joe Crowley, D-N.Y., called the subpoenas "nothing more than a political stunt and a gross abuse of power." The panel's actions show "just how far House Republicans' obsession with denying climate change really can go," Crowley said.