WASHINGTON (Reuters) -U.S. Senate Majority Leader Chuck Schumer and 22 other Democratic senators on Thursday asked the attorney general to investigate allegations of collusion and price fixing between the oil industry and the Organization of the Petroleum Exporting Countries (OPEC).

Earlier in May, the Federal Trade Commission gave the go-ahead to Exxon Mobil's $60 billion purchase of Pioneer Natural Resources, but barred former Pioneer CEO Scott Sheffield from Exxon's board on allegations he attempted to collude with OPEC to raise oil prices.

"These reports are alarming and lend credence to the fear that corporate avarice is keeping prices artificially high," the senators said in a letter to Attorney General Merrick Garland and his antitrust chief Jonathan Kanter.

"We therefore urge the Department of Justice to investigate the oil industry, to hold accountable any liable actors, and to end any illegal activities," the letter said.

White House Press Secretary Karine Jean-Pierre said she cannot comment on specific cases, and that "the President has made clear that any illegal collusion between big corporations is unacceptable and rips off hardworking families, including if it raises prices at the pump."

Sheffield coordinated efforts with U.S. shale oil producers to constrain their output and raise energy prices, the Federal Trade Commission said on May 2.

Widely considered the dean of U.S. shale because of his long tenure and blunt comments on industry output and spending, Sheffield used his influence "to align oil production across the Permian Basin in West Texas and New Mexico with OPEC+," the FTC added at the time.

A representative for Sheffield's lawyers referred to comments made earlier this week, when Sheffield asked the FTC to dismiss the ban. "At no time did government officials and Mr. Sheffield exchange competitively sensitive information," said Sheffield's counsel Cleary Gottlieb Steen & Hamilton.