House Oversight and Government Reform Chairman Darrell Issa is turning up the heat on the Obama administration after officials declined to comply with a document subpoena. In a letter Wednesday, the California Republican publicly threatened to begin contempt proceedings against Bureau of Alcohol, Tobacco, Firearms and Explosives acting Director Kenneth Melson if he does not obey the March 31 subpoena.

“The Department’s internal policy to withhold documents from what it labels pending criminal investigations may not deprive Congress from obtaining those same documents if they are pertinent to a Congressional investigation — particularly in a matter involving allegations that reckless and inappropriate decisions by top Justice Department officials may have contributed to the deaths of both U.S. and Mexican citizens,” Issa wrote in his letter to Melson, noting that the panel’s investigation is not concurrent with any Justice Department probes. “We are asking for documents that relate to decisions such officials made. Congress is legally entitled to all of these documents.”

Sen. Chuck Grassley (R-Iowa), ranking member on the Judiciary Committee, has also had a request in for documents since January.

Issa is investigating Project Gunrunner and Operation Fast and Furious, two operations where ATF allowed American guns to be smuggled into Mexico. ATF officials then tried to track where the illegal weapons were used in crimes.

Assistant Attorney General Ronald Weich responded on behalf of Melson following the April 13 deadline, according to the Issa letter, citing internal Justice Department policy for not releasing more information. The Justice Department did allow four documents be available for an “in camera” review at DOJ headquarters.

“Efforts by the Department of Justice and ATF to stonewall the Committee in its investigation by erroneously, but matter-of-factly, citing an internal department policy as a preventative measure for denying access to documents have only enhanced suspicions that such officials have played a role in reckless decisions that have put lives at risk,” Issa wrote. “The Committee continues to pursue this matter vigorously, in part, because concerned individuals have indicated they do not have confidence in the Department’s ability to review the actions of its own top officials.”