The Treasury Inspector General for Tax Administration, which performed the May audit that placed the Internal Revenue Service on the defensive in the ongoing political targeting scandal, is itself facing a lawsuit over possible violations of the Freedom of Information Act.

Cause of Action, a conservative-leaning government accountability group, last month filed suit in the U.S. District Court for the District of Columbia, charging TIGTA with failing to fully respond to an October 2012 FOIA request. The group had asked the IRS for documents relating to possible White House unauthorized access or disclosure of tax records belonging to political donors or candidates since 2006.

IRS referred the matter to TIGTA. The IG then responded in March that it could “neither confirm nor deny the existence of records” of communication between the White House and the IRS concerning such taxpayer information, citing certain privacy exemptions to FOIA.

Yet in a July letter to Sen. Charles Grassley, R-Iowa, responding to his request for an update on IRS investigations of political groups, TIGTA J. Russell George acknowledged eight such cases, Cause of Action said, and said his office had referred several to the Justice Department. “By revealing to Senator Grassley the existence of these communications,” the group added, “TIGTA has potentially violated FOIA with Cause of Action.”

A TIGTA spokesman said the agency cannot comment on pending litigation. A spokeswoman for Grassley also declined comment.

Anne Weismann, chief counsel for the nonprofit Citizens for Responsibility and Ethics in Washington, told Government Executive, “It’s not clear to me from Grassley’s letter that what TIGTA disclosed to Grassley is precisely what Cause of Action is seeking under the FOIA.” However, she added, “the letter does suggest that TIGTA may have responsive records from which they gathered that information for Sen. Grassley, over which they’re claiming an exemption to FOIA. There may be grounds for Cause of Action to challenge the withholding of the documents, but it’s not clear to me they’ve got the smoking gun.”

Angela Canterbury, director of public policy for the nonprofit Project on Government Oversight, took note of TIGTA’s invocation of the so-called Glomar response. The language “neither confirm nor deny” was used by the CIA in the 1970s to avoid confirming what later was revealed to be a secret salvage vessel designed by Howard Hughes to recover a sunken Soviet submarine. “I’m glad Cause of Action is pursuing the case,” Canterbury said. “The court will have to decide whether the principles of FOIA trump the Glomar claim.”

A Cause of Action spokeswoman said her group is awaiting a government response to the complaint, and expects one by mid-September.