Professor Paul R. McDaniel has performed an extremely valuable service in clarifying the relationship between trade and tax law. In particular, he has done so by pointing out that, to a large extent, the two spheres do not overlap, much less clash in their objectives. This makes sense because, fundamentally, the goal of trade law is to facilitate trade, while the goal of tax law is to raise revenue. Thus, for example, an ideal tariff under trade law is set at zero, but an ideal tax under tax law is set at some positive rate. It therefore should not be surprising that there is a large measure of non-overlap between trade and tax law.
Avi-Yonah, Reuven S. "Treating Tax Issues through Trade Regimes (Symposium: International Tax Policy in the New Millennium)." Brook. J. Int'l L. 26, no. 4 (2001): 1683-92.