Washington DC - House Democrats have launched an investigation into Donald Trump's alleged $1-billion quid pro quo offer to oil company executives last month.

On Monday, Democrats in the House Oversight Committee sent letters to nine oil execs asking for information on an April 11 meeting with Trump at Mar-a-Lago, in which the ex-president allegedly requested $1 billion in campaign donations in exchange for dismantling fossil fuel regulations.

"I write to request any information you may have about quid pro quo financial agreements related to U.S. energy policy that were reportedly proposed at a recent campaign fundraising dinner with ex-President Donald Trump at his Mar-a-Lago Club that you appear to have attended," Ranking Member Jamie Raskin of Maryland wrote in the letters.

"Media reports raise significant potential ethical, campaign finance, and legal issues that would flow from the effective sale of American energy and regulatory policy to commercial interests in return for large campaign contributions."

The Washington Post first reported on the 20-person meeting earlier this month. The outlet said Trump told the attendees at Mar-a-Lago that giving him $1 billion would be a "deal," as he would help them to avoid taxation and regulation.

Pro-fossil fuel actions Trump reportedly said he would take include ending the freeze on permits for new liquified natural gas (LNG) exports, authorizing more oil drilling in the Gulf of Mexico, and rescinding rules to reduce car emissions.

"Mr. Trump's unvarnished quid pro quo offer is especially troubling evidence in light of recent accounts that the 'US oil industry is drawing up ready-to-sign executive orders for Donald Trump aimed at pushing natural gas exports, cutting drilling costs and increasing offshore oil leases in case he wins a second term,'" Raskin said.

Donald Trump Trump hits back at FBI director over divisive "shrapnel" comment

"These preparatory actions suggest that certain oil and gas companies, which have a track record of using deceitful tactics to undermine effective climate policy may have already accepted or facilitated Mr. Trump’s explicit corrupt bargain."

House Democrats' letters went out to the CEOs of Chevron, ExxonMobil, Continental Resources, Chesapeake Energy, Occidental Petroleum, Venture Global LNG, Cheniere Energy, and EQT Corporation, as well as the American Petroleum Institute.

The execs are requested to provide information on the Mar-a-Lago meeting, including:

• Names of any company attendees
  
• Copies of any materials distributed
  
• A description of any policy proposals discussed
  
• A description of any campaign contribution discussions
• Copies of any company draft executive orders or policy paperwork
• Descriptions of any company efforts to provide financial support to Trump's campaign

Rhode Island Democrat Sheldon Whitehouse has expressed interest in launching a similar investigation in the Senate Budget Committee, which has subpoena powers.

"Trump’s offer of a blatant quid pro quo to oil executives is practically an invitation to ask questions about Big Oil’s political corruption and manipulation," Whitehouse said in a statement to The Guardian.