Democratic presidential candidate Sen. Bernie Sanders asked the Department of Justice Tuesday to investigate ExxonMobil for sowing doubt about climate change after the company's own scientists had confirmed and accepted the role of fossil fuels in global warming.

"We are writing concerning a potential instance of corporate fraud—behavior that may ultimately qualify as a violation of federal law," said Sanders' letter to Attorney General Loretta Lynch.

The letter cites an ongoing investigative series by InsideClimate News, which has revealed that Exxon scientists conducted rigorous climate research from the late-1970s to mid-1980s and warned top company executives about how global warming posed a threat to Exxon's core business. ICN's reporting also revealed that the company later curtailed its research program and instead led a long campaign to create doubt about climate science.

"Based on available public information, it appears that Exxon knew its product was causing harm to the public, and spent millions of dollars to obfuscate the facts in the public discourse," Sanders' letter said. "The information that has come to light about Exxon's past activities raises potentially serious concerns that should be investigated."

Sanders asked the DOJ to create a task force by Dec. 19 "to determine whether there is sufficient evidence to launch an official inquiry."

Two California congressmen—Democratic representatives Mark DeSaulnier and Ted Lieu—made a similar request last week. Their letter to the attorney general cited the ICN story and a separate investigation by the Los Angeles Times, which showed that Exxon studied how global warming could affect its Arctic operations.

"We request the DOJ investigate whether ExxonMobil violated RICO, consumer protection, truth in advertising, public health, shareholder protection or other laws," the congressmen's letter said, referring to the Racketeering Influenced and Corrupt Organizations law, which was how federal officials prosecuted tobacco companies in the 1990s.

Both Sanders and the California congressmen drew parallels between Exxon and the tobacco industry. Sanders' letter said the Exxon revelations "raise serious allegations of a misinformation campaign that may have caused public harm similar to the tobacco industry's actions—conduct that led to federal racketeering convictions."

A former DOJ attorney who helped prosecute the tobacco industry, Sharon Eubanks, told ThinkProgress that RICO action against fossil fuel companies is "plausible and should be considered."

Sen. Sheldon Whitehouse, a Democrat from Rhode Island who has endorsed the use of RICO against fossil fuel industries since May, made a similar argument in his weekly climate speech, delivered Tuesday on the Senate floor. He said there are "whole sections" of the tobacco court decision where "you can remove the word 'tobacco' and put in the word 'carbon,' and remove the word 'health' and put in the word 'climate,' and the parallel with the fossil fuel industry climate denial campaign is virtually perfect."

Martin O'Malley, another Democratic candidate for president, has also indicated his support for investigating Exxon. After the California congressmen wrote to the DOJ last week, O'Malley tweeted, "We held tobacco companies responsible for lying about cancer. Let's do the same for oil companies & climate change."

Hillary Clinton's campaign did not respond to a request for comment.

Click here to read the full letter.