垂直相關產業下國際商品課稅原則的選擇

THE CHOICE OF COMMODITY TAXATION PRINCIPLE IN A VERTICALLY RELATED INDUSTRY

Haufler et al.（2005）指出在線性需求函數下，不論是生產地或消費地課稅原則，最適商品稅稅率均為負值，且生產地課稅原則優於消費地課稅原則。本文考慮國際間存在的垂直相關產業現象，並重新檢視政府對商品課稅原則的決策問題。在線性需求函數的設定下，本文發現當第三國的上游廠商採取單一訂價方式時，消費地課稅原則（生產地課稅原則）下，最適商品稅稅率為一正值（負值），而消費地課稅原則的社會福利水準明顯優於生產地課稅原則。其次，當第三國的上游廠商採取差別訂價方式時，不論消費地課稅原則或生產地課稅原則，最適商品稅稅率均為正值；另一方面，當貿易成本較低（較高）時，生產地課稅原則的社會福利水準小於（大於）消費地課稅原則的社會福利水準。

Haufler et al. (2005) show that the optimal commodity tax rate under a linear demand function, regardless of the origin or destination principle, is negative; furthermore, the origin principle is welfare superior to the destination principle. This paper considers the phenomenon of vertically related industries and re-examines the choice of commodity taxation principles. We first show that, given a linear demand function, the optimal commodity tax rate under the destination (origin) principle is positive (negative) when the foreign upstream firm adopts a uniform pricing strategy; the destination principle is also superior to the origin principle. We also show that, when the foreign upstream firm adopts discriminatory pricing, the optimal commodity tax rate is positive, regardless of the origin or destination principle; when the trade cost is low (high), the origin principle is also inferior (superior) to the destination principle.