Meanwhile, Shinseki brushed aside calls for his resignation and got an unexpected political lifeline from House Speaker John Boehner following reports that 40 patients died because of delayed treatment at an agency hospital.
The American Legion and some in Congress have called for Shinseki's ouster following allegations of patient deaths at the Phoenix VA hospital due to delays in care and of a secret list the hospital kept of patients waiting for appointments to hide the delays.
The House Veterans Affairs Committee voted unanimously to subpoena all emails and other records in which Shinseki and other VA officials may have discussed destruction of what the committee called "an alternate or interim waitlist" for veterans seeking care in Phoenix.
A top VA official had told congressional staff last month that the "secret list" referred to in news reports may have been an "interim list" created by the hospital. And the committee had asked the VA on May 1 to answer why it was created, when it was destroyed, who authorized destruction and under what authority.
Shinseki answered in a letter Wednesday that VA employees used "transitory or interim notes ... for reference purposes" as they were moving information to the new electronic waitlist system. Regulations of the National Archives and Records Administration require that such notes be destroyed when they are no longer needed for reference, the VA says.
Dissatisfied with that response, the committee subpoenaed all documents relating to the destruction and gave Shinseki until 9 a.m. May 19 to produce them. The VA said in a statement that it will review the subpoena and respond.
Earlier Thursday, Shinseki told CBS that he sent inspectors to Phoenix immediately after he learned of reports about the deaths. "I take every one of these incidents and allegations seriously, and we're going to go and investigate," he said.
The VA also announced Thursday that Shinseki in recent days had ordered the Veterans Health Administration to do a "a face-to-face" audit over the next several weeks at all clinics at VA medical centers to make sure employees understand VA's policy and the need for continued integrity in managing patient access to care.
And at a Capitol Hill news conference, Boehner, R-Ohio, said: "I'm not ready to join the chorus of people calling on him to step down." He added that there is a "systemic management issue throughout the VA that needs to be addressed."
Shinseki announced last week that three officials at the Phoenix facility have been placed on leave while the VA inspector general investigates.
The Department of Veterans Affairs has long had a seemingly endless backlog and exceedingly long delays for treatment.
Boehner said the House is working on legislation that would give the head of the agency "more flexibility to fire people."
The White House has voiced support for Shinseki amid the calls for his ouster from the American Legion as well as from Republican Sens. Richard Burr of North Carolina, John Cornyn of Texas and Jerry Moran of Kansas. Veterans groups are split on whether he should resign.
White House spokesman Josh Earnest said President Barack Obama has full confidence in Shinseki. He said Shinseki shares the president's passion for living up to the commitment that the U.S. has made to its veterans.
Earnest told reporters traveling with Obama in California that the VA has made tremendous progress in reducing the case backlog. He said while the backlog is moving in the right direction, the White House won't be satisfied until it is eliminated.
The VA has acknowledged that 23 patients have died as a result of delayed care in recent years. The VA's Office of Medical Inspector said clerks at a Fort Collins, Colorado, clinic were instructed last year on how to falsify appointment records. Other problems have occurred in Pittsburgh, Atlanta and Augusta, Georgia.
Associated Press writers David Espo in Washington and Jim Kuhnhenn in Los Angeles contributed to this report.