Democrats are denying Republican lawmakers access to a trove of documents surrounding the impeachment proceeding against President Donald Trump unless they are supervised by Democratic staffers, according to a letter sent by all 21 GOP members of the House Foreign Affairs Committee.

Led by Rep. Michael McCaul (R., Tex.), the lawmakers protested a requirement by Rep. Adam Schiff (Calif.), the lead Democrat on the House Intelligence Committee, that a Democratic staffer be present when Republicans view the classified documents.

"Your staff claims that the only way we will have access to the transcripts is in your offices, during designated hours, under the personal supervision and monitoring of a majority staffer," the letter stated.

"It is outrageous and unjustifiable to deny us those basic documents, which are critical to our ability to meaningfully prepare for and participate in this investigation," the lawmakers wrote to Schiff. "We require the same access to the same documents in the same format, as is enjoyed by you and your staff."

The documents are being stored in a secure facility known as a SCIF (Sensitive Compartmented Information Facility). Under normal circumstances, all members of Congress are permitted to view classified documents at their will inside one of these rooms.

"I urge you to remedy this procedural injustice immediately, so that I am not forced to pursue public efforts to correct it, including by seeking a privileged vote on the House Floor," the lawmakers wrote.