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.

Last week, Amazon.com (NASDAQ: AMZN) filed a lawsuit in New York over the state's new law, which requires online retailers to collect sales tax from New York customers if the company has affiliates in the state soliciting sales for them.

Most state laws only require sales tax to be collected in a state if a company has a nexus, or physical presence there. Most states require purchasers of products who haven't paid sales tax on the items to voluntarily report the purchases to the state and pay use tax on them (the equivalent of sales tax). As you can imagine, in the government's eyes, this leaves plenty of tax money on the table as consumers rarely report these purchases to their home states and therefore avoid sales and use tax altogether.

New York's new law is a move to collect taxes on these sales, but it has angered Amazon.com and other companies. Affiliate programs are important to increase sales, as the "affiliates" are basically people and businesses who refer others to Amazon.com to make purchases. Amazon.com fought back, and now perpetual money-loser Overstock.com (NASDAQ: OSTK) is fighting back in its own way. Overstock is canceling its agreements with all of their affiliates in New York. If New York is going to use that affiliate relationship in order to impose sales tax on internet sales going to New York, then darn it, Overstock.com is going to show them!