WASHINGTON - Sen. Ted Cruz of Texas called on the Justice Department to back off the oil industry, joining other Republican lawmakers asking Attorney General Loretta Lynch to drop any investigations into whether oil companies committed fraud in past statements downplaying the science and impact of climate change.

"The Obama administration and its allies in state attorney general offices across the country are threatening to use the power of government to intimidate and ultimately silence companies and researchers who do not agree with the government's opinions about the allegedly harmful effects of climate change and what should be done about it," Cruz, an unsuccessful Republican presidential candidate, said in a statement. "This is an abuse of power and a direct assault on the First Amendment."

The Justice Department did not respond to a request for comment.

Cruz was among five Republican senators who signed a letter to Lynch, dated Wednesday, that called on her to halt investigations of whether oil companies suppressed research suggesting that burning fossil fuels contributed to rising global temperatures. The action against Lynch stems from testimony she gave before the Senate Judiciary Committee in March.

Asked by Sen. Sheldon Whitehouse, D-R.I., about what the Justice Department was doing on a "climate denial scheme," Lynch replied, "We have received information about it and have referred it to the FBI to consider whether or not it meets the criteria for what we could take action on. I'm not aware of a civil referral at this time."

Federal prosecutors have stayed quiet about potential oil industry investigations, but state attorneys general have not.

In March, a group of 18 attorneys general led by New York Attorney General Eric Schneiderman said they were considering launching investigations to see if companies misled their investors and the public. Exxon Mobil, the Irving-based oil giant,is already under investigation by the New York, U.S. Virgin Islands and California attorneys general.

The senators join the growing Republican chorus that climate change investigations amount to witch hunts against those on the other side of a scientific debate - even though the overwhelming consensus says mankind's use of fossil fuels is accelerating climate change.

Earlier this month, Texas Attorney General Ken Paxton intervened in the Virgin Islands investigation into Exxon Mobil, asking a state district judge in Fort Worth to block a subpoena issued by the territory's attorney general.

In their letter Wednesday, the senators described the attorneys generals' investigation as "disturbing confirmation that government officials at all levels are threatening … to silence debate on climate change."

The other signatories were Sen. Mike Lee, R-Utah, Sen. Jeff Sessions, R-Ala., Sen. David Perdue, R-Ga., and Sen. David Vitter, R-La.