The Justice Department's top watchdog said Thursday a newly released legal opinion undermines his independence and makes it more difficult to do his job.

Inspector General Michael E. Horowitz said the memo will delay access to grand jury, wiretap and other documents he needs to investigate problems at the Justice Department, the Drug Enforcement Administration, the FBI and elsewhere.

The legal memo, dated July 20 but made public Thursday, enshrines a process that in many instances puts the attorney general and her top deputy in charge of how much material their watchdog will get — and when.

"Congress meant what it said when it authorized inspectors general to independently access 'all' documents necessary to conduct effective oversight," Horowitz said. "Without such access, our office's ability to conduct its work will be significantly impaired, and it will be more difficult for us to detect and deter waste, fraud, abuse and to protect taxpayer dollars."

Horowitz added that he would work with lawmakers and top Justice Department officials to "promptly remedy this serious situation." And, he said, it may take legislation to make clear that federal watchdogs deserve sensitive materials from departments and agencies they oversee.

The dispute between the inspector general and the Justice Department leadership has been brewing for some time. Horowitz has testified to Congress repeatedly about his tug of war with DOJ officials to get records about a botched gun trafficking operation known as Fast and Furious — and more records involving sexual misconduct by agents at the DEA and FBI.

Some of those controversies were chronicled on NPR's All Things Considered. Horowitz also told lawmakers the Justice Department had slow-walked his access to material about whether lawyers had violated people's civil liberties in sweeping detentions after the Sept. 11, 2001, attacks; bulk surveillance programs by the FBI and DEA; and other counterterrorism tools.

Last year, congressional appropriators included a measure in the Justice Department budget supporting independent access for the inspector general. But this week's memo by Karl Thompson, principal deputy assistant attorney general, concluded that the intent of that provision was unclear. Lawyers are still analyzing the memo to see what impact it may have on other inspectors general across the U.S. government, and on whistleblowers who come to the IGs with paperwork that they say documents wasteful spending or abuses of power.

Lawmakers from both political parties almost immediately raised doubts about the legal memo, pointing out that before 2010, the FBI and other elements within the Justice Department routinely provided material to watchdogs they later began to withhold.

"The prospect of the Obama administration using this opinion to stonewall oversight, avoid accountability and undermine the independence of inspectors general is alarming," said Senate Judiciary Committee Chairman Charles Grassley, R-Iowa.

And Rep. Bob Goodlatte, the Virginia Republican who leads the House Judiciary Committee, said he would explore a legislative fix. Goodlatte said the legal memo and "efforts to reduce transparency will leave the Department of Justice vulnerable to mismanagement and misconduct."

In a statement, Justice Department spokeswoman Emily Pierce said, "The department has long held the position that the Inspector General should have access to all the information it needs to perform its essential oversight function."

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