According to a recently released report by the Congressional Research Service (CRS), entitled Access to Government Information in the United States:
The Constitution of the United States makes no specific allowance for any one of the co-equal branches to have access to information held by the others and contains no provision expressly establishing a procedure for, or a right of, public access to government information.
In general, interbranch disputes over access to information are political conflicts of the highest order. The federal courts, historically, have been reluctant to review and resolve such "political questions." Resolution is often reached through negotiation — reduction of the quantity of records initially sought, substitution of other information, alternative delivery mechanisms, or limitation of the number of individuals who will examine materials provided by another branch. Sometimes appeals to public opinion will pressure an information access deadlock to settlement. Congress can use its "power of the purse" to leverage its information access demands; federal courts rely upon a spirit of justice and fair play to sustain their orders for the production of information by another branch.
Americans have access to their own personal information collected by the federal government, public agency reports, federal advisory committee reports, and deliberations of agencies only via specific federal statutes. There is no Constitutional guarantee to this access.
Ironically, this CRS report is not freely available on a government site, but is hosted on the Federation of American Scientists’ CRS reports site. The Congressional Research Service produces reports at the request of members of Congress. They are some of the best research available about the legislative process. Congress cannot prevent the reports from being distributed to the public -- but there is no singular means of public access to these informative and important documents. The Law Librarian Blog and the Project on Government Oversight discuss this issue in greater detail.