Rep. Lamar Smith, chairman of the House Science Committee, escalated his confrontation over the climate probes of ExxonMobil by issuing subpoenas to two state attorneys general and several nongovernmental advocacy groups on Wednesday.

Smith (R-Tex.) announced the action in a news conference on Capitol Hill, saying the attorneys general of New York and Massachusetts were trying to criminalize the opinions of people and companies who hold alternative views on climate science.

Smith, joined by four Republican colleagues, demanded documents related to their discussions and investigations of Exxon. He harshly condemned what he called an attempt to suffocate the First Amendments rights of academic institutions, scientists and companies engaged in climate research.

"It is regrettable that two state attorneys general and several organizations continue to threaten legitimate scientific debate about climate change," Smith said during the news conference.

"The attorneys general have appointed themselves to decide what is valid and invalid regarding climate change. Attorneys general are pursuing a political agenda at the expense of scientists' rights to free speech."

The committee issued 10 subpoenas that order information be turned over within two weeks. Smith also did not preclude the possibility of hearings before the committee.

Eric Soufer, a spokesman for New York attorney general Eric Schneiderman, scoffed at the announcement, saying "Chairman Smith and his allies have zero credibility on this issue."

"The American public will wake up tomorrow morning shaking their heads when they learn that a small group of radical Republican house members is trying to block a serious law enforcement investigation into potential fraud at Exxon," Soufer said. "This Attorney General will not be intimidated or deterred from ensuring that every New Yorker receives the full protection of state laws."

Ken Kimmell, president of the Union of Concerned Scientists, which is among the groups singled out by Smith, called the subpoenas an abuse of power.

"By attempting to interfere with the attorneys general investigations, Chairman Smith directly undermines efforts to hold ExxonMobil accountable for misrepresenting climate science," Kimmell 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."

A spokeswoman for Massachusetts Attorney General Maura Healey suggested Smith and the Republican-led committee was acting at the "behest of Big Oil" and called the subpoenas an affront to states' rights.

"This isn't a fight about the First Amendment because the First Amendment doesn't protect false and misleading speech," said spokeswoman Cyndi Roy Gonzalez. "Our office seeks only to understand what Exxon's own scientists knew about the impact of burning fossil fuels on climate change and on Exxon's business and assets, when they knew it, and what they told the public."

The action by the Republican-controlled committee reflects the contentious, partisan escalation of a fight over Exxon and the fossil fuel industry's role in decades of climate change denial.

"I'm sure this type of harassment won't stop here," said Randy Weber, a Texas Republican and chairman of the Energy Subcommittee, referring to the climate probes. He said the attorney generals and groups' goal is to intimidate and put out of business anyone that disagrees with their political views.

"We've seen these tactics with this administration's environmental regulations. They will all shut down large portion of our economy," Weber said.

"Now it appears the same tactics are being employed by the attorneys general effectively trying to shut out debate and scare Americans into supporting this president's partisan environmental agenda."

Exxon has been under investigation by attorneys general in New York, Massachusetts and California as part of a coalition of 17 attorneys general formed earlier this year to support urgent action on climate change and investigate fossil fuel companies that spread doubt about climate science. (The attorney general of the U.S. Virgin Islands recently announced the withdrawal of a subpoena and a scaling back of its investigation of Exxon.)

Exxon has come under intense scrutiny following the publication of an investigative series by InsideClimate News that revealed the company participated in cutting edge climate change science beginning in the late 1970s that showed the dangers posed by increasing atmospheric CO2 caused primarily by the burning of fossil fuels.

Similar independent findings were later published by a team based at the Columbia Journalism School in partnership with the Los Angeles Times. A report by the Union of Concerned Scientists concluded ExxonMobil was not alone in developing early knowledge of climate change and later spreading disinformation about the science.

Several nongovernmental advocacy groups came out swinging hours before the announcement of the subpoenas in response to Smith's renewed demand last week to turn over documents related to their involvement in the multiple investigations of ExxonMobil.

The groups have refused to cooperate and gone on the offensive, demanding that members of the committee disclose their connections with Exxon and other fossil fuel industry-funded groups.

Greenpeace and 350.org have called out Smith, a Texas Republican who has repeatedly expressed his belief that climate change is not real or human-caused, over his acceptance of campaign money from the fossil fuel industry. It has also assailed Smith's attack of a NOAA report that contradicted the notion that global warming has slowed in the last decade.

Since 2008, Smith has received $675,597 from the fossil fuel industry, including $19,500 from ExxonMobil, according to the two groups. At the same time, Smith has led a series of inquiries of climate scientists and organizations—including NOAA—questioning their research or methods.

Neither Smith nor the committee responded to requests for comment.

The tense standoff comes in response to a third round of letters sent by Smith last week to six NGOs and the two state attorneys general. The letters demand documents Smith is now seeking via subpoena.

In May, 13 Republican members of the committee sent letters to 17 state attorneys general and eight environmental groups and nonprofits. They demanded thousands of records on whether the groups and the state attorneys general worked together in coordinating the probes.

Greenpeace and 350.org said that Smith and the committee's demands infringe on their First Amendment rights.

"Based on the partisan tone of the July 6th letter, we are concerned that the true purpose of the Committee's requests is not to examine the science of climate change, but rather to silence those who would shine a spotlight on the role of the fossil fuel industry, and ExxonMobil in particular, in undermining climate science and blocking and delaying meaningful action on climate change," the organizations' attorney, Abbe David Lowell, wrote in a letter.

Lowell said Greenpeace and 350.org have volunteered to talk with the committee but the offer was never acknowledged. The groups have also sent the committee a series of questions requesting information about whether committee members have ties to, or have had discussions with, Exxon or other fossil fuel companies.