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The United States Constitution requires that in order for either chamber to conduct business, a quorum of voting members must be present. Currently, there are 435 voting members in the House of Representatives and 218 members must be present in order to constitute a quorum for business. The Senate has 100 members and 51 senators must be present to constitute a quorum.
The same section of the US Constitution also gives both chambers the absolute power to determine the rules of their proceedings. The rules in each chamber govern all aspects of Congressional business within that chamber and there are no joint rules covering procedure in both chambers.
Since the 108th Congress (2003–2004) the Rules of the House of Representatives have included provisions for convening a subset of the members to act in the case of a terrorist attack. Rule XX, clause 5(c)(1) states in part as follows:
If the House should be without a quorum due to catastrophic circumstances -- (A) until there appear in the House a sufficient number of Representatives to constitute a quorum among the whole number of the House, a quorum in the House shall be determined based upon the provisional number of the House[.]
This rule requires that a number of actions be taken before a provisional quorum can be established. These include a 72-hour-call for a quorum, a report to the Speaker of the House and Majority and Minority leaders from the sergeant-at-arms of a “catastrophic quorum failure,” the Speaker’s announcement of the report to the House, and a further call of the House for at least 24 hours to establish a quorum. Once these conditions are met then a provisional quorum would be established based on the number of members who responded to the second call of the House.
The constitutionality of this rule revision was raised at the time as to whether it violated the quorum provision that a majority of each chamber needed to be present to conduct business. The question was put to the House, which voted in favor of this rule.
The Standing Rules of the Senate have no equivalent provision. Senators Durbin and Portman have recently introduced S.Res.548 to allow members to vote remotely rather than coming to the Senate chamber to cast their vote and Senate practice does not require the presence of a quorum in the chamber while conducting daily business.
Prepared by Margaret Wood
Senior Legal Reference Librarian
 U.S. Const. art. I, § 5, https://www.govinfo.gov/content/pkg/GPO-CONAN-2017/pdf/GPO-CONAN-2017-6.pdf.
 Rules of the House of Representatives, https://www.govinfo.gov/content/pkg/HMAN-116/pdf/HMAN-116-houserules.pdf.
 Cong. Research Serv., RL 33610, A Retrospective of House Rules Changes Since the 104th Congress through the 109th Congress 41 (updated Mar. 8, 2012), https://crsreports.congress.gov/product/pdf/RL/RL33610.
 Standing Rules of the Senate, https://www.govinfo.gov/content/pkg/CDOC-113sdoc18/pdf/CDOC-113sdoc18.pdf.
 Senate Resolution 548, https://www.congress.gov/bill/116th-congress/senate-resolution/548
 Riddick’s Senate Procedure: Precedents and Practices 1041-42, https://www.govinfo.gov/content/pkg/GPO-RIDDICK-1992/pdf/GPO-RIDDICK-1992-111.pdf.
Last Updated: 12/30/2020