An anonymous reader writes "Last week Slashdot reported on the blockage of a union website by Telus, a leading Canadian ISP. Since that story, the company has restored access but the fallout continues. The move may lead to new ISP regulations in Canada and a study by the OpenNet Initiative has found that by blocking the union site, Telus also blocked an additional 766 websites including a breast cancer fundraising site." From the article: "While there are a number of different ways to block access to Web sites, the method Telus chose to block the Voices for Change site -- blocking its IP address -- produced massive collateral filtering. Filtering by IP address is efficient since ISPs can quickly and effectively block access to the target site using their existing routing technology. Many ISPs already block certain IP addresses to combat spam and viruses. Large networks, like Telus, have mechanisms in place to block IP addresses almost instantaneously, simply by updating their routers with a "block list" of addresses. However, it is common for many different, unrelated Web sites to share the same IP address."