A prominent U.S. senator has demanded a probe into allegations that the federal agency charged with guarding drug safety is attempting to discredit an agency whistleblower.

Senate Finance Chairman Charles Grassley, a Republican wrote the Health and Human Services Department Wednesday to request an investigation of defaming phone calls about Food and Drug Administration, FDA, safety officer David Graham. The phone calls were received by the Government Accountability Project, a public interest group that defends whistleblowers.

Dr. Graham alleges the calls are a response to his congressional testimony last week during which he said the FDA has abandoned its watchdog role for a cozy relationship with the pharmaceutical industry, a charge the agency denies.

He told Congress the FDA has left consumers virtually defenseless against unsafe prescription drugs. He also said five drugs on the market, besides the recently withdrawn pain medication Vioxx, need further review.