Scattered around the U.S. Capitol complex are a series of Sensitive Compartmentalized Information Facilities, or SCIFs, which are typically used to hold Top Secret information.

But today in these deeply secure settings are a series of unclassified documents—items dealing with the Iran nuclear deal that are not secret, but that the Obama administration is nevertheless blocking the public from reading.

The Obama administration delivered 18 documents to Congress on July 19, in accordance with legislation requiring a congressional review of the nuclear deal. Only one of these documents is classified, while the remaining 17 are unclassified.

Yet many of these unclassified documents cannot be shared with the public or discussed openly with the press. The protocol for handling these documents, set by the State Department and carried out by Congress, is that these unreleased documents can only be reviewed ‘in camera’—a Latin term that means only those with special clearance can read them—and must be held in various congressional SCIFs.

Most staffers were hesitant to discuss—let alone share—a number of these documents, even though they’re not classified, because they require security clearances to view. By mixing a classified document with unclassified documents, critics of this arrangement contend, important facts are being kept from the public just as Congress is deciding whether to support or oppose the Iran deal.

“The unclassified items… should be public. This is going to be the most important foreign policy decision that this Congress will make,” a Republican Senate aide told The Daily Beast. “This is the administration that once said it would be the most transparent administration in history. They’re not acting like it.”

“Many in Congress view the administration’s tactic of co-mingling unclassified documents with classified documents and requiring congressional staffers to have secret clearances just to view certain unclassified documents as an attempt by the administration to limit open debate,” a second senior Republican congressional staffer said.

Among the 17 unclassified documents are important texts related to the Iran nuclear deal: One document, titled “Elements of Iran’s R&D Plan,” is based on the “safeguards confidential plan [between] Iran and the IAEA,” or International Atomic Energy Agency, a State Department official said, and so it can’t be released publicly. The document describes how Iran’s research and development on its nuclear program, including on its centrifuges, could progress over time.

Other unclassified documents may be diplomatically sensitive: One is a letter from the foreign ministers of France, Germany and the U.K. to Secretary of State John Kerry; another is a letter from Kerry to the three foreign ministers and his Chinese counterpart as well.

The set includes a discussion paper written before the final agreement, on how sanctions would be dealt with in the interim. Yet another is a draft statement by the U.S. government, to be issued on a future Iran deal implementation day.

Bloomberg View’s Eli Lake and Josh Rogin previously reported the existence of the 18 documents submitted by the Obama administration to Congress, as well as some descriptions of what the set contained.

The Iran nuclear deal is unlike other arms control agreements “because it’s so complex and has so many moving parts,” said Jeffrey Lewis, director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies. “It goes into jaw-dropping detail.” So it’s not a complete surprise that there might be some sensitive ancillary documents to go along with the arrangement. Iran might not want the particulars of its nuclear research program in full public view, for instance.

The unreleased, unclassified documents are informative for Congress but not for public consumption, the State Department contends.

“Some of the documents are the types of documents which, like State Department cables and other internal USG documents, we would not post publicly but would share with Congress in appropriate circumstances. Others are documents that, while not part of the [Iran nuclear agreement] itself, pertain to it and we were clear with the other P5+1 members and Iran that we would be sharing those documents with Congress, and we have,” a State Department official said.

Added the official, “Congress has every document that we have, and every Member of Congress and every staff [member] with the necessary security clearance can review all of the documents.”

Some Democrats were supportive of the administration’s hush-hush approach. The documents are part of a sensitive diplomatic process involving Iran’s nuclear program, they argue, so it’s not surprising that there are some restrictions to the level of transparency the government will allow.

“The essential elements to make the decision on the deal are out there,” a senior Democratic aide said. “I don’t think there’s a lack of transparency or discussion on [the Iran deal], because you’ve had very detailed briefings and every member of Congress has been able to view these documents… The way they are stored is consistent and not unreasonable, and I don’t think there’s anything nefarious.”

Open-government advocates, on the other hand, were appalled that unclassified documents this important were being kept both from public view—and, in a real way, from serious congressional scrutiny.

“Keeping unclassified documents in a SCIF is overkill, even if the documents are sensitive or confidential. They simply don’t need the kind of sophisticated protection against clandestine surveillance that SCIFs are intended to provide,” said Steven Aftergood, a senior research analyst at the Federation of American Scientists, working to reduce government secrecy.

“The primary obstacle to congressional review that is created by this arrangement is the requirement to physically be present in the SCIF. Members of Congress cannot review the material in their offices, or share it with trusted colleagues or with subject matter experts. It is a significant hindrance to review,” he added.

Congress passed a law called the Iran Nuclear Agreement Review Act, also known as Corker-Cardin, requiring the administration to formally submit the Iran nuclear deal, an unclassified verification assessment with any secret annexes, and other relevant materials to Congress.

The intention of that provision was for unclassified materials to be freely available so that an open debate on the public interest could occur. Members of Congress are pointing out that this is not what is happening—and are urging the Obama administration to allow their release.

“A lot of both documents and discussion that have been held in a classified setting doesn’t have classified characteristics to it… to the extent that many [documents aren’t classified,] they should be made totally public, as far as I’m concerned, so that the public can evaluate for themselves,” Democratic Senator Bob Menendez told The Daily Beast.

Republican Senator Bob Corker, the chairman of the Senate Foreign Relations Committee, agrees. His spokesperson told The Daily Beast that Corker “believes that the administration should make these unclassified documents available to the public so the American people can see the details of the Iran nuclear deal.”

—with additional reporting by Alexa Corse and Noah Shachtman