During 1973-1978, respondent chewing gum manufacturer, which is based in Chicago, sold its products in Wisconsin through a sales force consisting of a regional manager and various "field" representatives, all of whom engaged in various activities in addition to requesting orders from customers. Wisconsin orders were sent to Chicago for acceptance, and were filled by shipment through common carrier from outside the State. In 1980, petitioner Wisconsin Department of Revenue concluded that respondents in-state business activities during the years in question had been sufficient to support imposition of a franchise tax. Respondent objected to the assessment of that tax, maintaining that it was immune under 15 U.S.C. 381(a), which prohibits a State from taxing the income of a corporation whose only business activities within the State consist of "solicitation of orders" for tangible goods, provided that the orders are sent outside the State for approval and the goods are delivered from out-of-state. Ultimately, the State Supreme Court