Access to Congressionally Mandated Reports Act This bill requires the Government Publishing Office (GPO) to establish and maintain a publicly available online portal containing copies of all congressionally mandated reports. A federal agency must submit a congressionally mandated report and specified information about the report to the GPO between 30 and 45 calendar days after submission of the report to either chamber or to any congressional committee or subcommittee. Upon the written request of the chair of a congressional committee or subcommittee to the GPO, a report submitted to that committee or subcommittee shall not be submitted or published on the portal. Federally chartered corporations and the Government Accountability Office are excluded from the requirements of this bill. The Office of Management and Budget must issue guidance to federal agencies on the bill's requirement for agencies to submit copies of congressionally mandated reports and related information to the GPO.