Five months after asking the Food and Drug Administration to explain its secret e-mail surveillance of its employees, a prominent Senate Republican says he is getting no answers.

After hearing nothing for months, Grassley said, he spoke with Commissioner Margaret Hamburg on May 24. She promised a detailed response to numerous questions raised by Grassley and Rep. Darrell Issa (R-Calif.), chairman of the House Oversight and Government Reform Committee. A response would be timely, she said, according to Grassley aides.

But the senator says he has heard nothing. According to an e-mail exchange between Grassley’s staff and FDA officials, the agency cannot provide answers to the lawmakers because the Obama administration is still reviewing its response.

“After four months of pushing on our end, at last, the FDA commissioner herself indicated that a response was on the way,” Grassley said in a statement.

“Then the FDA abruptly switched gears and said an unnamed official in the [Obama] administration is reviewing the response. This puts us back to square one, and it’s not a good development from an administration that was supposed to be the most transparent in history.”

FDA spokeswoman Erica Jefferson said Tuesday that the agency “will be responding directly to Senator Grassley.”

Grassley demanded in January that Hamburg disclose who authorized the monitoring, how many employees were targeted and whether the agency obtained passwords to their personal e-mail accounts, allowing their communications on private computers to be intercepted. Grassley also wants to know whether the monitoring is still going on.

The Post reported in January that the scientists and doctors filed a federal lawsuit against the FDA, alleging that the government violated their constitutional privacy rights by intercepting their communications on Yahoo, Gmail and other private accounts to monitor activity they say was lawful.

The employees’ communications with Congress, the Equal Employment Opportunity Commission, the inspector general’s office that oversees the FDA and the Office of Special Counsel were intercepted. The special counsel, the independent federal agency that represents whistleblowers, also has opened an investigation into the monitoring.

The FDA tried but failed to have criminal charges brought against the whistleblowers for disclosing sensitive business information. The employees were fired, demoted or harassed.

Grassley has warned the FDA that interfering with a congressional inquiry is illegal.

The agency has warnings on its computers, visible when users log on, that employees have “no reasonable expectation of privacy” in any data passing through or stored on the system, and that the government may intercept any such data at any time for any lawful government purpose.

But attorneys for the employees have said the warning itself is illegal because it does not ensure that anyone preparing a complaint to an agency that investigates wrongdoing has a right to keep their private communications confidential.

The plaintiffs had challenged the safety and effectiveness of devices used in detecting colon cancer, breast cancer or other medical problems. Most of the devices were approved by supervisors after the scientists recommended against approval.The inspector general’s office for the Department of Health and Human Services concluded twice that there was no evidence of criminal misconduct by the scientists.