Update: April 2018
In October 2017, Pennsylvania passed a law that took effect March 1, 2018. Like Washington’s law, Pennsylvania’s requires that marketplace facilitators or remote sellers with more than $10,000 in sales in the state either collect sales tax or follow certain use tax notification and reporting requirements.
Earlier: January 2013
In December 2011, the Pennsylvania Department of Revenue issued a bulletin clarifying that state law requires an out-of-state retailer to collect sales tax if it has property stored or distributed through warehouses in the state (regardless of whether the retailer owns the warehouses) or if it uses affiliated sales agents to direct sales to its website.
Amazon operates six fulfillment centers in Pennsylvania and has sales affiliates in the state. It began collecting sales tax on orders shipped to Pennsylvania residents on September 1, 2012.