Westendorp v R, [1983] 1 S.C.R. 43 was a decision of the Supreme Court of Canada on the scope of the federal Parliament's criminal law power under section 91(27) of the Constitution Act, 1867. A unanimous Court found that a municipal by-law that prohibited standing in the street for the purpose of prostitution was in the nature of a criminal law prohibition and therefore ultra vires of the provincial constitutional authority