Protecting the environmental agenda of President Obama was the primary motivator for a group of Democratic attorneys general to join together and investigate oil companies and nonprofits, a conservative group said Tuesday.

The Energy and Environment Legal Institute released a letter sent by New York Attorney General Eric Schneiderman and Vermont Attorney General William Sorrell to Iowa Attorney General Tom Miller that showed that influencing federal environmental regulations was top of mind for the organizers of the attorneys general.

The goal of the group is "to highlight the importance of climate change to the citizens of our states, our work defending Clean Power Plan … and the formation of an Attorneys General climate change and energy coalition committed to working together to take effective investigative and legal steps to address the risks that climate change poses to all of our citizens," the letter states.

Eventually, 17 Democratic attorneys general joined together to use the powers of their offices to investigate oil companies and their affiliated interest groups.

E&E Legal Institute Executive Director Craig Richardson said the letter is more proof the attorneys general are conspiring to use their offices for political purposes and abusing their power.

"This letter makes inescapable the fact that the AGs' goal was to defend and extend Obama's environmental agenda," he said. "That is a political cause, which the AGs seek to extend by improper means, circumventing the proper, democratic political process."

Last week, the group released the Common Interest Agreement between the attorneys general that showed attempts by the attorneys general to keep public records secret.

"It is unprecedented to have the top state law enforcement officers waging a political war on behalf of the president at the cost of the First Amendment protections they are charged with upholding," said E&E Legal Senior Legal Fellow Chris Horner. "This letter lays bare that the purpose of their investigations was to launch a political campaign to silence critics of the administration."

The states whose attorneys general signed the agreement are: California, Connecticut, Washington, Massachusetts, Illinois, Maryland, Maine, Minnesota, New Hampshire, New Mexico, New York, Oregon, Rhode Island, Virginia and Vermont as well as the District of Columbia and the U.S. Virgin Islands.

The agreement has come under intense scrutiny following investigations started by Schneiderman, Massachusetts Attorney General Maura Healey and Virgin Islands Attorney General Claude Walker.

Walker subpoenaed Exxon Mobil and the Competitive Enterprise Institute to find out what the company and the group knew about the effects of greenhouse gas emissions on climate change. Following intense blowback amid accusations of trying to criminalize free speech, Walker eventually withdrew the subpoenas.

Healey and Schneiderman were subpoenaed by House Science, Space and Technology Committee Chairman Lamar Smith for documents related to their subpoenas served to Exxon Mobil. Smith made similar accusations against them as were made against Walker, that they were criminalizing free speech and science that could have shown climate change isn't real.

Healey and Schneiderman have not backed down and refused to comply with the subpoenas.

Most of the other Democratic attorneys general have not taken any action on the pact.