A group of progressive U.S. senators on Monday pushed Robert F. Kennedy Jr., secretary of the Health and Human Services Department, to disclose what he and President Donald Trump discussed with pharmaceutical executives at recent private dinners as the industry pressures the new administration to end Medicare drug price negotiations.

In a letter to Kennedy, Sens. Elizabeth Warren (D-Mass.), Ron Wyden (D-Ore.), and Bernie Sanders (I-Vt.) pointed to Wall Street Journalreporting from last month on the millions of dollars that healthcare industry executives spent to dine with Trump at his Mar-a-Lago club in Florida ahead of his inauguration.

Kennedy, according to the Journal, “attended several of the dinners, but largely stayed quiet as Trump and others talked.”

Warren, Wyden, and Sanders wrote to Kennedy that “the dinners may have served as an opportunity for Big Pharma to gain insider access to both you and President Trump” and asked the HHS chief to reveal information about the meetings with industry executives, including how many there have been since the November election and whether Medicare drug price negotiations or other critical matters were discussed.

“Big Pharma stands to profit immensely from a second Trump administration, especially if they can convince you and President Trump to abandon policies like Medicare drug price negotiations and patent reform that would save Americans hundreds of billions of dollars on lifesaving drugs,” the senators wrote. “Indeed, the executives that attended these dinners have called on him to ‘pause drug negotiations’—negotiations that are expected to save taxpayers $100 billion by 2032.”

“You owe the American public an explanation for why you took part in PhRMA’s influence-peddling events with President Trump, what happened at these meetings, and whether they will affect your commitment to ensuring that Americans receive the relief they deserve from high drug prices,” the senators added.

The Journal reported that the CEO of Pfizer, which pumped $1 million into Trump’s inaugural committee, was among the executives who attended the private Mar-a-Lago dinners. Eli Lilly’s chief executive also joined at least one of the dinners.

Though Kennedy, an anti-vaccine conspiracy theorist, has vocally criticized Big Pharma and its political influence, the industry did not lobby against his nomination to lead HHS, which oversees the Medicare drug price negotiations that began during the Biden administration.

Last month, the head of the pharmaceutical industry’s biggest lobbying group and several pharma CEOs met with Trump as part of a campaign to weaken the price negotiations, which threaten drugmakers’ ability to jack up prices at will.

The negotiations have yielded significant results, but Trump’s Centers for Medicare and Medicaid Services—an agency within HHS—has signaled it is open to altering the program.

“The Trump administration’s statement is far from an embrace of drug price negotiation,” Wyden and other senators warned earlier this year, “and appears to be opening the door to changes that could undermine Medicare’s ability to get the best price possible on drugs.”