The Wall Street Journal is reporting today that Amazon.com (NASDAQ: AMZN) is likely facing additional sales tax challenges in eight states besides New York. The New York issue has been well-publicized, with the state imposing new rules that would make Amazon subject to sales tax there because of the presence of affiliates.

Normally, sales tax must be collected by a retailer only if that retailer has nexus (usually a physical presence) in a state in which an item is sold. In the past, nexus generally meant that the company had physical operations there, so the change in New York law, which now includes the presence of affiliates, is a big change. But courts also have ruled that the physical presence test is not the only way to create nexus.

The new wrinkle in the sales tax issue has to do with the distributions centers Amazon has around the country. The WSJ says [subscription required] that there are eight states with Amazon warehouses or distribution centers, but that Amazon has avoided collecting sales tax in those states by operating the facilities as subsidiaries of the parent company. Sales tax laws have permitted this exception when a facility is part of a separate legal entity.