A group of Republican state attorneys general is standing up for oil giants over an investigation into whether companies like Exxon Mobil misled the public about the risks of climate change.

"Using law enforcement authority to resolve a public policy debate undermines the trust invested in our offices and threatens free speech," the Republicans wrote.

ASSOCIATED PRESS Alabama Attorney General Luther Strange and other Republicans came to the oil industry's defense in a letter sent to fellow state attorneys generals.

The coalition, called "AGs United for Clean Power," was formed in late March following reports by InsideClimate News and the Los Angeles Times that found Exxon executives were aware of the climate risks associated with carbon dioxide emissions, but funded research to cover up those risks and block solutions.

In a more recent investigation, the Washington-based Center for International Environmental Law uncovered documents that show the oil industry, including Humble Oil (now ExxonMobil), was on notice about the potential role of fossil fuels in CO2 emissions no later than 1957 and “shaping science to shape public opinion” even earlier, in the 1940s.

New York Attorney General Eric Schneiderman -- who subpoenaed Exxon in January over the allegations that it lied to the public and its investors -- said in a March speech announcing the coalition that the science on climate change is clear.

"We know what's happening to the planet," Schneiderman said. "There is no dispute, but there is confusion, and confusion sowed by those with an interest in profiting from the confusion and creating misperceptions in the eyes of the American public that need to be cleared up."

Mike Segar / Reuters New York Attorney General Eric Schneiderman speaks at a news conference to announce a state-based effort to combat climate change, March 29, 2016.

GOP Attorneys General say in their Jun. 15 letter that the Democratic-led investigation of the oil industry "raises substantial First Amendment concerns."

They disregard studies that suggest the consensus among scientists is as high as 97 percent. Instead, the authors write that "a vigorous debate exists in this country regarding the risks of climate change and the appropriate response to those risks." Actions indicating one side of the debate should fear prosecution "chills speech," they said.

The First Amendment defense has been a go-to for the industry in its fight to keep internal climate documents buried. Suzanne McCarron, ExxonMobil’s vice president for public and government affairs, said in March the coalition's effort was “politically motivated" and the allegations against her company were “an attempt to limit free speech."

But Schneiderman pointed out that the First Amendment "does not give you the right to commit fraud." "We are pursuing this as we would any other fraud matter," he said in March. "You have to tell the truth. You can't make misrepresentations of the kinds we've seen here."

In many ways, the oil companies’ cover-up of climate risks rivals that of the tobacco industry misleading the public about the health risks associated with smoking. Not only did both stretch back decades, they each raised questions about a company's constitutional right to free speech.

In the case of big oil, former Vice President Al Gore said time is of the essence. "We do not have 40 years to continue suffering the consequences of the fraud allegedly being committed by the fossil fuel companies where climate change is concerned," he said at the March event.

Mike Segar / Reuters Former U.S. Vice President Al Gore speaks at a news conference to announce a state-based effort to combat climate change, March 29, 2016.

In addition to echoing industry claims about free speech, Strange and his co-authors warn their Democratic counterparts that the issue is a two-way street -- that "any fraud theory requiring more disclosure of Exxon would surely require more disclosure by 'clean energy' companies."

"If it is possible to minimize the risks of climate change, then the same goes for exaggeration," the letter reads. "If minimization is fraud, exaggeration is fraud."

May Boeve, executive director of environmental group 350.org, was among those who slammed the Republican Attorney Generals' letter. She said Exxon refuses to "turn from its destructive deception on climate change," even in the face of record-breaking temperatures.

"Whether it's trying to block Attorney General [Maura] Healey's investigation in Massachusetts or orchestrating coordinated attacks from Republican attorneys general across the country," Boeve said in a statement, "it's clear that Exxon's only interest is in maintaining the status quo of its business model -- planet and people be damned."