Sen. Bernie Sanders (I-Vt.) plans to announce his opposition Friday to President Obama’s nominee to lead the Food and Drug Administration, citing questions about Dr. Robert M. Califf’s commitment to lowering pharmaceutical prices.

Sanders, who is mounting a surprisingly strong bid for the Democratic presidential nomination against Hillary Rodham Clinton, told The Washington Post that he spoke by phone last week with Califf and came away unconvinced that he is the right person for the job of commissioner.

“At a time when millions of Americans cannot afford to purchase the prescription drugs they need, we need a new leader at the FDA who is prepared to stand up to the pharmaceutical companies and work to substantially lower drug prices,” Sanders said in a statement. “Unfortunately, I have come to the conclusion that Dr. Califf is not that person.”

Califf, a prominent cardiologist and longtime researcher at Duke University, joined the FDA earlier this year as a deputy commissioner. When Obama announced his nomination for the top post, Califf drew praise from some health groups, but his close ties to the pharmaceutical industry have been a source of controversy.

A 2014 financial disclosure showed Califf’s salary at Duke was underwritten partly by funding from large drug makers such as Eli Lilly, Novartis and Merck. He also reported receiving fees from a range of other pharmaceutical companies, which a government spokesman said were donated to charities.

Sanders’s decision to oppose the nomination comes as Clinton has taken some recent positions at odds with Obama that bring her into line with the more progressive wing of the Democratic Party.

In recent days, Clinton has come out against a major trade deal being pushed by Obama and against the Keystone XL oil pipeline -- positions that both Sanders and former Maryland governor Martin O’Malley, another Democratic hopeful, took months ago.

On the campaign trail, Sanders has been pushing a plan to curtail “runaway prescription drug prices,” a phenomenon he attributes in part to the hundreds of millions of dollars the pharmaceutical industry spends on lobbyists and campaign contributions.

Sanders’s plan would allow the federal government to negotiate drug prices with pharmaceutical companies and reduce barriers to the importation of lower-cost drugs from other countries, including Canada.

Sanders also wants to encourage wider availability of more generic drugs and impose tougher penalties on drug companies that commit fraud.

“The greed of the pharmaceutical industry is a public health hazard to the American people,” Sanders said in his statement. “That has got to change.”