(The Hill) — Rep. Darrell Issa (R-Calif.) on Friday described the National Labor Relations Board as a “rogue agency” for its response to subpoenas he issued for documents related to the panel’s legal complaint against airplane manufacturer Boeing.

The NLRB has yet to provide any documents to Issa, chairman of the House Oversight and Government Reform Committee. The board’s general counsel said Friday in a letter to Issa that the NLRB was concerned about releasing any documents prematurely.

That provoked a harsh response from Issa, who said the NLRB’s hesitation put into question “the integrity of NLRB and its leadership.”

“The National Labor Relations Board and Acting General Counsel Lafe Solomon have thus far failed to comply with a lawful subpoena,” Issa said in a statement released Friday. “This refusal by NLRB to abide by the law further heightens concerns that this is a rogue agency acting improperly.”

In his letter, Solomon said the NLRB continues to be “gravely concerned about the adverse effect any premature release of certain documents subject to the subpoena would have on the rights of the parties to this case to have a fair trial.”