With the revelation that as much as 90% of ivory traded on the Internet is illegal, eBay has stopped sales of the product across borders. 

The move, which applies only to cros-border sales and not within individual countries, was announced at a CITES (Covention on International Trade in Endangered Species) conference.
Different countries apply their own laws to internal ivory trade, but sellers need to produce certification proving their ivory isn't poached in order to sell across borders. With the Internet, however, this formality often falls away, opening the door to illegal trading.
Certification will be given to ivory that was in existence before the 1974 CITES treaty, or from stocks that receieved one-time exemptions.