Lawmakers exacted repeated pledges from the Food and Drug Administration chief Thursday that he supports the right of agency whistleblowers to alert Congress to drug-safety and other concerns.

The FDA’s treatment of whistleblowers has long been of concern to members of the House and Senate, stemming in part from allegations the agency has retaliated against employees who spoke out about safety issues with the now-withdrawn painkiller Vioxx, antibiotic Ketek and other drugs.