Oregon constitution
Article IV: legislative branch
Section 10

(3) A regular session, as described in subsection (1) of this section, may be extended for a period of five calendar days by the affirmative vote of two-thirds of the members of each house. A session may be extended more than once. An extension must begin on the first calendar day after the end of the immediately preceding session or extension except that if the first calendar day is a Sunday, the extension may begin on the next Monday.