A senior Democratic senator is calling for an investigation into potential insider trading by fossil-fuel billionaires close to the Trump administration, after a Guardian investigation raised questions about an unusual share buying spree.

Robert Pender and Michael Sabel, the founders and co-chairs of Venture Global, a liquefied natural gas (LNG) company headquartered in Virginia, bought more than a million shares worth almost $12m each, just days after meeting with senior Trump officials in March.

The meeting included Chris Wright, the energy secretary, who days later granted the company an export license essential for its expansion plans in Europe, the Guardian reported last week.

“Dirty oil and gas bucks are fueling the Trump Administration, which should outrage all of us. This latest reporting portrays a pattern of pay-to-play donations and favorable actions by the administration,” said Jeff Merkley, senator for Oregon and senior member of the Senate appropriations and budget committees.