A Plenary Assembly of the Conference is to be held at least once a year (c. 453). Additional sessions may, with approval of the Administrative Committee, be convened by the President when such are deemed necessary or opportune. The President of the Conference presides at the Plenary Assemblies (c. 452§2).When in session, under terms and conditions set forth in its Bylaws, this Assembly possesses the full authority of the Conference. All officers and committees of the Conference, therefore, are answerable to
Members In a spirit of collegial concern for the needs of the Church, especially in the United States, all members of the Conference have a responsibility to attend Plenary Assemblies unless impeded for serious reason.
The Apostolic Nuncio, though not a member of the USCCB, may be present at all sessions of the general assembly and shall be invited by the President to address the general membership (c. 450§2).
Non-members of the Conference may, with the express approval of the Administrative Committee, attend the public sessions of the plenary assembly as official observers and may also be granted the opportunity to speak. Guests and those involved in the work of the Conference are authorized to attend a particular session by the Conference President or the General Secretary. Members of the media may be present for public sessions of the Plenary Assembly with the approval of the Conference President in consultation with the Chairman of the Committee on Communications.
---from USCCB Statutes and Bylaws