Sen. Joe Manchin III is calling for an investigation of “pay to play” allegations regarding a scientific panel that shaped the Food and Drug Administration’s thinking on painkillers and that, according to the organizer’s e-mails, was funded by major pharmaceutical companies that put up as much $25,000 to attend a meeting.

In a letter to FDA Commissioner Margaret Hamburg, Manchin requested that the agency turn over to his office a long list of documents, including the names of all the companies that paid to attend the panel’s meetings, how much they paid, and e-mails between the organizers and agency officials.

Manchin (D-W.Va.) has been pressing the agency to put stricter limits on hydrocodone — one of the key ingredients in Vicodin and Lortab — because of their addictive power and widespread availability.

Pharmacy companies and others have resisted the effort, saying in part that more restrictions could unfairly put the drugs out of reach for patients who need them.

“It is a shame that some of these companies were able to influence the FDA’s decision with a $25,000 contribution, while West Virginian families are destroyed by the addiction these pills cause,” Manchin said in a statement.

He said he is “calling for a full investigation to see how far this goes. If these allegations are true, they explain why it has taken the FDA almost a year to reach a decision to reschedule hydrocodone.”

In calling for the investigation, Manchin cited a Washington Post report this week that drug companies paid as much as $25,000 to attend meetings of the scientific panel, according to e-mails among organizers.

The meetings were arranged by two academics and were attended by FDA officials overseeing painkillers. They amounted to what one agency officials described as “an essential collaborative effort.”

FDA officials said they were “unaware of any improprieties” associated with the meetings of the group. An FDA spokesman declined to comment on Manchin’s request.