(Bloomberg) -- Environmental groups are pressuring presidential debate monitors to ask Donald Trump whether he made promises to oil industry executives in exchange for $1 billion in campaign donations. 

“Voters deserve to hear exactly what Trump promised Big Oil CEOs,” the Sierra Club, League of Conservation Voters, Climate Power and other green groups wrote to CNN’s Jake Tapper and Dana Bash.

Trump sought $1 billion in contributions during an April meeting with oil and gas executives at his Mar-a-Lago resort, prompting congressional investigations into whether he made a “quid pro quo” offer to change policy for money. 

“When all eyes are on the party nominees on June 27, we hope you will take the opportunity to help voters learn more about President Trump’s promise to top oil executives and dig into both candidates’ records on climate,” said the letter, which was sent Thursday. “As climate change makes extreme weather disasters more frequent, destructive, and expensive, we are counting on you to ensure the voters know where President Biden and former President Trump stand.”

Trump and President Joe Biden are scheduled to square off at the first presidential debate June 27 at CNN’s studio’s in Atlanta.

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