WASHINGTON (AP) — A group advising the Food and Drug Administration on medical issues abruptly dropped four experts from a panel on prescription painkillers after concerns emerged about apparent ties to the pharmaceutical industry.

The panel gathered in Washington on Wednesday for its first meeting, tasked with developing recommendations for the FDA on combating the problem of painkiller abuse and misuse. But four doctors listed on the panel's initial roster were dropped before the meeting.

"We are not moving forward" with their nominations, said a spokeswoman for the National Academies of Sciences, Engineering and Medicine, which organized the panel. She declined to elaborate on the decision.

The national academies advise the federal government on medical, scientific and related issues. The FDA requested a report on the use of opioid painkillers after coming under fire for not doing enough to reduce fatal overdoses tied to the drugs, which have risen for the last 15 years.

Federal advisers are supposed to be vetted for financial ties that can influence their judgment. Senator Ron Wyden of Oregon sent a letter Friday to the academies' leadership noting that two of the panel nominees had also served in professional societies that receive funding from drugmakers. Wyden has protested industry influence on federal expert panels before.

One of the experts, Dr. Gregory Terman, said he was dismissed Tuesday afternoon by phone. He said he was told the decision was made because his nonprofit group, the American Pain Society, receives funding from drugmakers.

"I responded that I'm very proud of my relationship with the American Pain Society, we're the only professional society in the world that thinks of pain science as priority No. 1," said Terman, in an interview with The Associated Press.

Wyden's letter notes that the society has a "corporate council" of pharmaceutical manufacturers — including Purdue Pharma, Pfizer Inc. and Teva Pharmaceuticals — that contributed at least $132,500 to the group, according to online materials. Terman has served on the group's board of directors since 1998.

A second panelist cited in Wyden's letter — Mary Lynn McPherson — received grants and residencies worth at least $300,000 that were sponsored or paid for by opioid drugmakers, according to a review of her work history cited by congressional staff. McPherson, who specializes in hospice and end-of-life care, is currently a professor at the University of Maryland School of Pharmacy.

A university spokesman said in a statement that McPherson's funding was "not controlled or influenced in any way by the funding source."

"Any implication that Dr. McPherson or her work has been compromised by association with pharmaceutical companies is deeply misguided."

The national academies also dropped two other physicians specializing in pain care.

Wyden notes in his letter: "My staff has been unable to thoroughly examine all of the members given the limited time available to review the provisional committee members."

The highest-ranking Democrat on the Senate Finance Committee, Wyden has raised similar concerns about conflicts of interest on a pain panel organized by the National Institutes of Health. Last week he asked the director of NIH to turn over documents on how those experts are vetted.