2 U.S.C. § 27 - U.S. Code - Unannotated Title 2. The Congress § 27. Change of place of meeting

Whenever Congress is about to convene, and from the prevalence of contagious sickness, or the existence of other circumstances, it would, in the opinion of the President, be hazardous to the lives or health of the members to meet at the seat of Government, the President is authorized, by proclamation, to convene Congress at such other place as he may judge proper.