US President Donald Trump and Attorney General William Barr have been accused of ordering federal employees to ignore subpoenas issue by Congress.
A senior Democrat has accused the Trump administration of a "massive, unprecedented, and growing pattern of obstruction" for ordering federal employees not to comply with congressional investigations.
"Both President Trump and Attorney General (William) Barr are now openly ordering federal employees to ignore congressional subpoenas and simply not show up - without any assertion of a valid legal privilege," House Oversight Committee chairman Elijah Cummings has said in a statement.
The Justice Department on Wednesday rebuffed the House Oversight and Reform Committee, which had sought to interview an official involved in the Trump administration's decision to put a citizenship question on the 2020 US Census.
The department said Civil Rights Division deputy assistant attorney general John Gore would not participate in a deposition scheduled for Thursday if he could not have a Justice Department lawyer at his side.
The committee had offered to allow a lawyer to sit in a different room.
Cummings said the subpoena issued to Gore was adopted on a bipartisan basis and that there was no privilege asserted by the White House or the Justice Department that would preclude him from appearing.
"This is a massive, unprecedented, and growing pattern of obstruction," Cummings said, warning the federal employees to think "very carefully" about their own legal interests in refusing to comply with the panel's requests.