At least three government agencies obstructed independent investigations into alleged wrongdoing, according to a letter sent to congressional oversight leaders Tuesday by 47 independent federal watchdogs.

The 47 Inspectors General (IG) said the Justice Department, the Peace Corps, and the Chemical Safety Board withheld information from their offices, citing various privileges.

"We have learned that the Inspectors General for the Peace Corps, the Environmental Protection Agency (in his role as Inspector General for the Chemical Safety and Hazard Investigation Board) and the Department of Justice have recently faced restrictions on their access to certain records available to their agencies that were needed to perform their oversight work in critical areas," the letter said. "These restrictive readings of the IG Act represent potentially serious challenges to the authority of every Inspector General and our ability to conduct our work thoroughly, independently, and in a timely manner."

The officials said that watchdogs from other agencies have also "faced similar obstacles to their work, whether on a claim that some other law or principle trumped the clear mandate of the IG Act or by the agency’s imposition of unnecessarily burdensome administrative conditions on access."

Inspectors General are appointed to provide independent oversight of federal agencies and investigate whistleblower claims.

"Refusing, restricting, or delaying an Inspector General's access to documents leads to incomplete, inaccurate, or significantly delayed findings or recommendations, which in turn may prevent the agency from promptly correcting serious problems and deprive Congress of timely information regarding the agency's performance," the letter states.

According to the letter, the Justice Department originally refused to hand over documents in three Inspector General investigations.

In a statement to the Washington Post, Justice Department spokesman Brian Fallon said the department did not block the IG’s investigation.

"Because the documents at issue included grand jury material, credit reports, and other information whose dissemination is restricted by law, it was necessary to identify exceptions to those laws to accommodate the inspector general’s request," he said. "But everything sought was provided."

In the case of the Peace Corps, the letter said the agency failed to provide information on sexual assaults of its volunteers.

A Peace Corps spokeswoman told news outlets the agency is "committed to working with the Inspector General to ensure rigorous oversight while protecting the confidentiality and privacy of volunteers who are sexually assaulted."

Congressional oversight leaders criticized the stonewalling efforts.

"This is an administration that pledged to be the most transparent in history. Yet, these non-partisan, independent agency watchdogs say they are getting stonewalled. How are the watchdogs supposed to be able to do their jobs without agency cooperation?" Sen. Chuck Grassley (R., Iowa) said in a statement. "Inspectors General exist to improve agencies and get the most bang for every tax dollar. This letter underscores the need for congressional review and possibly legislative action."