WASHINGTON: The US Senate budget committee on Thursday launched a probe of 18 domestic oil producers about any efforts to illegally coordinate oil prices with the Organization of the Petroleum Exporting Countries (OPEC).

The producers the committee is probing include Exxon Mobil , Chevron and ConocoPhillips. None of those companies immediately responded to requests for comment.

Interest in possible collusion among oil companies with production groups spiked after the US Federal Trade Commission (FTC) in May barred former Pioneer Natural Resources CEO Scott Sheffield from Exxon’s board on allegations he attempted to collude with OPEC to raise oil prices. The FTC made the move as it approved Exxon’s $60 billion purchase of Pioneer.

Sheffield has denied the FTC’s allegations.

Senator Sheldon Whitehouse, a Democrat and the chairman of the Budget committee, called for the probe of the companies.

“In view of the findings against Sheffield, I seek to understand whether other oil producers operating in the United States may also have been coordinating with OPEC and OPEC+ representatives concerning oil production output, crude oil prices, and the relationship between the production and pricing of oil products,” Whitehouse said in a statement.

The American Petroleum Institute (API) industry group called the probe an “election year stunt.”

API spokesperson Bethany Williams said: “This is yet another election-year stunt to distract from misguided policies as the administration continues to look to foreign producers to meet growing demand for affordable, reliable energy.”

President Joe Biden, a Democrat, hopes to win reelection in November. Whitehouse, of Rhode Island, is running for a fourth term in the US Senate.