Eric Shinseki
U.S. Veterans Affairs Secretary Eric Shinseki in a file photo. Reuters

Frustrated by a lack of cooperation from the Department of Veterans Affairs, the House Veterans Affairs Committee is ramping up its investigation into charges of poor medical care -- and a possible cover-up. While the House investigation goes on, VA Secretary Eric Shinseki will testify next Thursday before the Senate Committee on Veterans Affairs.

The House committee voted unanimously at a special meeting Thursday to subpoena Shinseki and other senior VA leaders who, committee members say, have not fully cooperated with its probe of allegations by four whistleblowers that as many as 40 veterans died while waiting to be seen by doctors.

The subpoena covers all emails by VA executives from April 9 to the present that may have discussed the destruction or disappearance of a so-called secret list of veterans waiting for care at the Phoenix VA Health Care System.

“It is unfortunate that we have to come to this decision, but we did not do so without substantial justification,” committee Chairman Jeff Miller, R-Fla., said in his opening statement. “The last few weeks have been a model of VA stonewalling which precipitated the need for a subpoena.”

Shinseki, a retired four-star general and former Army chief of staff, said repeatedly this week that VA will take swift action if any employees have been involved with delays of medical appointments and subsequent cover-ups at VA hospitals.

The VA released a statement Thursday afternoon saying in part, "Secretary Shinseki has directed the Veterans Health Administration (VHA) to complete a nationwide access review. The purpose of this review is to ensure a full understanding of VA’s policy and continued integrity in managing patient access to care. As part of the review during the next several weeks, a national face-to-face audit will be conducted at all clinics for every VA Medical Center (VAMC)."

"I am angry," Shinseki told NBC News Wednesday. “We're going to do something about it, to get to the bottom of it and to the best of our abilities to ensure it never happens again."

As part of his search for answers, Miller sent a letter to Shinseki last week urging the department to preserve possible evidence related to the Phoenix allegations.

Miller’s letter also addressed the VA’s admitted shredding of a waiting list that department officials have said may be the “secret” list cited by the Phoenix VA whistleblowers, including two physicians.

Miller warned Shinseki that if VA did not fully respond to his requests by the end of the work day Wednesday (May 7), he would “not hesitate to convene an emergency meeting of the committee to formally subpoena all requested information.”

In his response on Wednesday afternoon just hours before Miller’s deadline, Shinseki said the VA was “conducting robust internal reviews to evaluate appointment scheduling procedures and patient care in Phoenix.”

“It does not appear that PVAHCS [Phoenix Veterans Affairs Health Care System] patients who were not able to be seen within 90 days were handled consistently prior to the arrival of the current leadership team in 2012,” Shinseki wrote.

A House committee spokesman told International Business Times that the deadline for VA to respond to the subpoena is May 19 at 9 a.m. Then the committee will review the materials provided by VA and determine the next steps.

Meanwhile, the VA controversy is widening. Accusations by whistleblowers that VA managers falsified scheduling data now also involve facilities in Texas and Colorado.

On Monday the American Legion, the nation's largest veterans organization, called for Shinseki to resign, and a Denver Post editorial Wednesday said “Shinseki ought to go.”

Legislators are split on the issue. GOP Sens. John Cornyn of Texas, Jerry Moran of Kansas and Richard Burr of North Carolina have called on Shinseki to step down. But Sen. Jim Inhofe, R-Okla., Republican ranking member of the Armed Services Committee, said he still backs the VA chief. “I’ve been working with Gen. Shinseki for many years. He’s made great sacrifices for his country, including loss of limb. So I’m not about to call for his resignation.”

House Speaker John Boehner, R-Ohio, also said Thursday, "I'm not ready to join the chorus of people calling for him to step down."

On the Democratic side, Sen. Bernie Sanders, the Vermont independent who chairs the Senate Veterans Affairs Committee, still supports the secretary, as does Senate Majority Leader Harry Reid of Nevada.

President Barack Obama, too, has expressed his continued confidence in the embattled secretary.