A probe of the Food and Drug Administration’s e-mail surveillance of its employees widened Wednesday as the independent federal agency representing whistleblowers opened an investigation.

The FDA secretly monitored the private e-mail accounts of six scientists and doctors who had warned Congress and the White House that medical devices they were reviewing were approved or pushed toward approval despite safety concerns.

Among the communications, made on agency computers, were e-mails the employees wrote to the Office of Special Counsel, which reviews disclosures about government wrongdoing and retaliation against those who report it.

On Wednesday, attorneys for the employees and two prominent Republican lawmakers asked the special counsel to investigate whether the device reviewers’ communications with the office, the Equal Employment Opportunity Commission and the inspector general that oversees FDA operations were protected under federal whistleblower laws. The attorneys and lawmakers say the e-mails were confidential and should not have been intercepted.

The special counsel’s involvement follows a federal lawsuit the scientists and doctors filed against the FDA in January, alleging that the government violated their constitutional privacy rights by intercepting their personal Gmail accounts to monitor activity they say was lawful.

“The confidentiality of these communications was broken,” said Stephen M. Kohn of the National Whistleblowers Center, whose firm is representing the plaintiffs. “As part of their official duties, they have the right to disclose confidential concerns. Employees throughout the government can work on these matters on paid time.”

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. The FDA tried but failed to have criminal charges brought against the whistleblowers for disclosing sensitive business information. The agency then fired or harassed them, the lawsuit says.

Special Counsel Carolyn Lerner warned against any government monitoring of e-mail communications with her office. “Monitoring employee e-mails with Office of Special Counsel or Congress could dissuade employees from making important disclosures,” Lerner said in a statement.

She encouraged federal agencies to review their policies to ensure that they are not monitoring any disclosures — or impending disclosures — by whistleblowers of wrongdoing.

Health and Human Services Secretary Kathleen Sebelius, asked about the monitoring at a Senate budget hearing Wednesday, said that the FDA plans to cooperate with the special counsel’s investigation.

“While I certainly share your concerns about the potential for retaliation against whistleblowers,” she told Sen. Charles E. Grassley (R-Iowa), the FDA “needs to have protections about proprietary information.”

Grassley and House Oversight and Government Reform Committee Chairman Darrell Issa (R-Calif.) have opened their own probes into the e-mail monitoring, warning the FDA that interfering with a congressional inquiry was illegal. On Wednesday, they appealed to Lerner’s office to investigate apparent discrepancies in when the surveillance began.

The FDA said last week that it began the surveillance in April 2010 to investigate allegations the employees, who worked for the Office of Device Evaluation, leaked confidential information to the public. But documents they obtained showed contents of several e-mails from January 2009 between one device reviewer, Paul Hardy, and a congressional aide.

“The fact that the FDA is in possession of an e-mail from [Hardy’s] personal account to Congress from January 2009 — more than one year prior to the date on which FDA admits commencing surveillance — suggests that the FDA may have accessed Hardy’s personal e-mail to retrieve prior communications that were not necessarily sent from a government computer,” the senators wrote.

A Justice Department spokesman, Charles S. Miller, declined to comment.

The FDA posts warnings on its computers, visible when users log in, 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 Kohn said the warning is illegal because it does not ensure that employees who are preparing complaints to agencies that investigate wrongdoing have a right to confidential communications.