Mitchell said in a letter to Shinseki, dated Friday and released this week, that he's heard complaints from other members of Congress about requests for information going unanswered or taking too long.
"Our subcommittee has an obligation, on behalf of the nation's veterans, to examine the VA's efforts to address the problem," Mitchell said. "We cannot, however, conduct our work without access to appropriate witnesses and appropriate information from the Department of Veterans Affairs."
Katie Roberts, a VA spokeswoman, said in a statement Tuesday that the VA takes seriously its responsibility to provide Congress with information. She said the VA offered to make Janet Kemp, the VA's national suicide prevention coordinator, available for the hearing.
"We have had a very positive relationship with Congress," Roberts said.
Suicides among veterans of Iraq and Afghanistan have been a lingering problem. Last year, the Army saw a record number. Available data through 2007 shows a higher rate of suicide among those who served in the recent conflicts and left the military, compared to the general population.
To combat the problem, the VA hired thousands of new suicide prevention coordinators and created a suicide prevention hot line.