A senior Senate Republican has launched an investigation into the Food and Drug Administration’s secret e-mail monitoring of scientists who warned that unsafe medical devices were approved over their objections, saying whistleblowers often are treated “like skunks at a picnic.”

In a five-page letter released Wednesday, Sen. Charles E. Grassley (R-Iowa) demanded that FDA Commissioner Margaret A. Hamburg disclose who authorized the monitoring, how many employees were targeted and whether the agency obtained passwords to personal e-mail accounts, allowing communications on private computers to be intercepted. Grassley also wants to know whether the two-year surveillance campaign is ongoing.

His probe comes in response to Monday’s Washington Post report on a lawsuit filed in U.S. District Court in Washington last week by six current and former FDA scientists and doctors. They allege that the government violated their constitutional privacy rights by monitoring personal communications they said were lawful.

“I write to express my concerns over your agency’s treatment of whistleblowers as a result of their disclosures to Congress, and specifically disclosures to my office,” Grassley, the ranking member on the Finance Committee, told Hamburg. “Whistleblowers . . . are often treated like skunks at a picnic.”

Federal investigators reached a similar conclusion this week about four civilian whistleblowers at Dover Air Force Base who reported missing body parts and other management failures at the mortuary that handles the remains of fallen soldiers. The independent Office of Special Counsel concluded that the workers’ supervisors retaliated against them for going public, trying to fire two and placing the others on suspension and indefinite leave.

FDA spokeswoman Erica Jefferson said Hamburg “will respond directly” to Grassley. Documents that the whistleblowers obtained under the Freedom of Information Act show FDA officials thought the reviewers disclosed confidential information when they communicated concerns to congressional staffers, the White House, the Equal Employment Opportunity Commission and the special counsel’s office.

FDA computers post a warning when employees log in to a computer that they should have “no reasonable expectation of privacy” in data passing through or stored on the system. But reviewers deny they shared information improperly and contend the monitoring was a blatant form of retaliation. Information gathered from e-mail eventually contributed to the harassment or dismissal of all six workers, the suit alleges.

Grassley and his staff have investigated the FDA for years as controversies over medical device and drug safety have swept through the agency. He is a longtime advocate of protections for whistleblowers.

Grassley warned Hamburg that it is illegal for a government agency to interfere with an employee’s right to air concerns to members of Congress. He said the FDA had “no evidence” that one of the device reviewers, Paul J. Hardy, disclosed confidential business information, yet fired him after he exchanged e-mails with congressional staff.

Hardy was the lead reviewer for a machine designed to search for signs of breast cancer. Hardy refused approval. “The data showed the device was no good,” he said in an interview. “It wasn’t even as good as what was already on the market.”

Several of his managers agreed, but the machine was put on the market anyway after a manager intervened and requested second opinions from other scientists, documents show. When Hardy was preparing the label, he proposed language showing the device was not as effective as those already on the market. But he was told by his supervisor to delete the data from the label or suffer disciplinary action, Hardy said.

A commissioned officer in the U.S. Public Health Service, Hardy was fired in November after a negative performance review prevented him from being promoted.

Public Health Service officers do not have protection from retaliation under federal whistleblower laws, an exemption the lawsuit, the special counsel’s office and Grassley are seeking to change.

“It is troubling to me to see your Agency actively pursue the dismissal of an employee . . . simply because you ‘cannot trust him,’ ” Grassley wrote to Hamburg. Hardy’s dismissal “directly contradicts” her testimony during confirmation hearings to protect whistleblowers by “creating a culture that enables all voices to be heard,” he wrote.