Call it a tit for tat over subpoenas, one that escalates an ongoing spat over what the biggest U.S. oil company knew and when it knew it.

House Science, Space and Technology Committee Chairman Lamar Smith (R-Tex.) said Wednesday his committee was issuing subpoenas to the New York and Massachusetts state attorneys general, who have issued their own subpoenas as part of probes into whether ExxonMobil misled the public and investors about what it knew about the dangers of climate change decades ago.

ExxonMobil and its defenders have asserted that the company has merely been exercising its free speech rights with respect to climate change.

In a joint news conference, Rep. Randy Weber (R-Tex.) called the attorneys general a “posse” and said “since when did it become a crime to hold an opinion?” He said the attorneys general “have veered away from enforcing the law to environmental activism.”

Smith said the committee was also issuing subpoenas to eight environmental organizations to obtain documents related to their efforts to encourage the state attorneys general to pursue their Exxon investigations.

That triggered outcries from environmental groups, who said the committee subpoenas were designed to inhibit the very free speech the House members were claiming to protect.

“Chairman Smith’s subpoena is an abuse of power that goes way beyond the House Science Committee’s jurisdiction and amounts to nothing more than harassment,” Ken Kimmell, president of the Union of Concerned Scientists, said in a statement. “It’s also just plain wrong to investigate a nonprofit for doing its job — in this case, providing public officials with science and evidence to hold fossil fuel companies accountable for deception on climate change, one of the world’s most pressing problems.”

Kimmell said that the Union of Concerned Scientists, in response to a letter from Smith last week, had just offered to brief the committee’s staff about UCS activities.

“UCS has been completely transparent about our efforts to inform state prosecutors,” Kimmell added. “We won’t apologize for trying to expose this deception.”

He said Smith was abusing the House Science Committee’s subpoena power.

“It’s beyond ironic for Chairman Smith to violate our actual free speech rights in the name of protecting ExxonMobil’s supposed right to misrepresent the work of its own scientists and deceive shareholders and the public,” he said.

But five GOP members of the committee said that the attorneys general were abusing their subpoena power to intimidate ExxonMobil.

“Every individual corporation … has the right to conduct scientific research and formulate opinions, their own opinions, free from the threat of prosecution,” Weber said.

ExxonMobil has done research about climate change since the 1970s and 1980s, but the company has extended financial support to a variety of organizations that have cast doubt on the links between man-made emissions of greenhouse gases and climate change.

Several years ago, ExxonMobil chief executive Rex Tillerson acknowledged that climate change was real and that a carbon tax would be the best way to address greenhouse gas emissions.

The state attorneys general are looking into whether the oil giant knew with certainty about the links between fossil fuels and climate change. The attorneys general are looking at whether ExxonMobil, by not adequately disclosing the risks of climate change, misled investors about the dangers of the company’s own product and therefore failed to provide material information.

“Prosecutors shouldn’t be in this business,” said Rep. Darin LaHood (R-Ill.). “It really is an abuse of power.”

But Eric Soufer, spokesman for  New York Attorney General Eric Schneiderman, said, “the singular purpose of these [state] investigations is to determine whether Exxon committed serious violations of state securities fraud, business fraud, and consumer fraud laws.”

Soufer said that the Science committee “has no authority to interfere with these state law enforcement investigations, and whether they issue a subpoena or not, this Attorney General will not be intimidated or deterred from ensuring that every New Yorker receives the full protection of state laws.”

The environmental group said that Smith, who has already sent three rounds of letters to attorneys general and environmental groups, was motivated by the campaign contributions he has received from oil and gas companies. It said Smith has issued more subpoenas in less than three years as chairman than the committee had issued in its entire 54 years of existence.

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