The U.S. Department of Health and Human Services admitted in a Wednesday letter to the National Archives and Records Administration that one its senior executives, Marilyn Tavenner, likely deleted some of the emails subpoenaed by Congress ten months ago regarding the botched Healthcare.gov rollout.

The admission resulted in a scathing response from Rep. Darrell Issa (R-Calif.), chairman of the House Oversight and Government Reform Committee, who called the destroying of government emails a “violation of federal law.”

Medicare chief Marilyn Tavenner testifies on Capitol Hill in Washington, Tuesday, Nov. 5, 2013, before the Senate Health, Education, Labor, and Pensions Committee hearing as the panel seeks reassurances about problems with the debut of the Affordable Care Act. Republicans on the committee emphasized their longstanding criticism of the law, citing examples of cancellations and increased costs while raising questions about cyber-security for healthcare.gov. (AP Photo/J. Scott Applewhite)

“Today’s news that a senior HHS executive destroyed emails relevant to a congressional investigation means that the Obama Administration has lost or destroyed emails for more than 20 witnesses, and in each case, the loss wasn’t disclosed to the National Archives or Congress for months or years, in violation of federal law,” Issa said in a statement. “It defies logic that so many senior Administration officials were found to have ignored federal record keeping requirements only after Congress asked to see their emails.”

“Just this week, my staff followed up with HHS, who has failed to comply with a subpoena from ten months ago. Even at that point, the administration did not inform us that there was a problem with Ms. Tavenner’s email history. Yet again, we discover that this Administration will not be forthright with the American people unless cornered,” he continued.

Tavenner, who is the Medicare chief, took a lot of the initial heat after Healthcare.gov got off to a horrific start in 2013.

HHS claims it will likely be able to recover “some but not all” of the requested emails, MSNBC’s Alex Seitz-Wald reports.

HHS argues Tavenner received an extremely high volume of emails on a daily basis and she routinely deleted emails after forwarding them to members of her staff for retention purposes. Because she didn’t do this every single time, the department claims, some of the emails were deleted and lost.

In the letter to the National Archives and Records Administration, HHS Records Management Director Kathleen Cantwell says the department is taking steps to improve their records retention process.

HHS CMS Letter on Missing Emails by Alex Seitz-Wald