A group targeted by Democratic attorneys general in a climate change investigation hit back at subpoenas they call "unlawful and un-American" in a new video posted Tuesday.

The Competitive Enterprise Institute fought off a subpoena from U.S. Virgin Islands Attorney General Claude Walker earlier this year. Walker's subpoena was sent to the group to try and get information about ExxonMobil's donations to the climate change-doubting think tank from 1997 to 2007.

Walker believed he was trying to investigate what ExxonMobil knew about how fossil fuels impact climate change and when, but CEI leaders say it was a battle over freedom of speech.

"No American should fear being singled out and harassed by a government official who takes a different point of view on public policy questions," says Kent Lassman, president of the group in the video.

CEI and its lawyers put enough pressure on Walker to cause him to rescind his subpoena and they're now seeking formal punishment for Walker.

Walker's actions were a part of a larger plan led by New York Attorney General Eric Schneiderman.

Schneiderman and Massachusetts Attorney General Maura Healey have both subpoenaed ExxonMobil to find out if the company defrauded its shareholders by lying about climate change. Attorneys general from California, Connecticut, Washington, Illinois, Maryland, Maine, Minnesota, New Hampshire, New Mexico, Oregon, Rhode Island, Virginia and Vermont as well as the District of Columbia have all promised to join in the effort in some way.

Many critics say the attorneys general are using the powers of their office to attack the right to free speech of climate deniers.

"Our first reaction was 'Hell no! This thing is one unconstitutional fishing expedition,'" CEI General Counsel Sam Kazman said in the video. "The real thing that they're after is to shut down the global warming debate."