OpenNet Initiative: Bulletin 010

Telus Blocks Consumer Access to Labour Union Web Site and Filters an Additional 766 Unrelated Sites

August 2, 2005
Last Updated: August 2, 2005

- Background
- Methodology & Results
- Observations
- About the OpenNet Initiative

On July 25, 2005, Canadian Internet Service Provider (ISP) Telus blocked subscribers' access to a Web site set up by an employee labor union intended to publicize the union's views about its dispute with Telus. In addition, the OpenNet Initiative's (ONI) research shows that Telus's decision to block traffic to the Internet Protocol (IP) address of the site caused collateral filtering of at least 766 additional, unrelated Web sites. Telus restored access to the IP address hosting the sites on July 28, 2005, while appearing to maintain an option to block any sites it chooses.


Telus is one of Canada's largest ISPs, with over one million customers. The company temporarily blocked its subscribers from accessing a union-run Web site in an escalating labour dispute with the Telecommunications Workers Union. Subscribers attempting to access the site were not given a message informing them that their ISP was blocking the site, but rather found it simply inaccessible, as if the site itself had been taken down or a network error had prevented a connection. Telus confirmed that it blocked access to the Voices for Change website (, on the basis that the "website ha[d] posted illegal information." (1) Telus blocked access to the site on July 25, 2005 and restored access on July 28, 2005.

Tests undertaken by the ONI on July 27, 2005 showed that Telus's blocking extended to far more than the single targeted site. Telus's filtering also blocked 766 additional, unrelated sites with domain names hosted on the same server as the blocked site. These sites included, an engineering company;, a breast cancer fundraising site;, an alternative medicine site based in Australia; and, a Colorado based electronic recycling company.

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. As a consequence, IP-based blocking has the side effect of restricting access to every other site hosted at the same IP address as the blocked site. Thus, the standard practice of Web hosting providers to maintain many sites at one IP address can result in collateral damage when an ISP, like Telus, blocks one of those sites by filtering the shared IP address.

The ONI has investigated cases of collateral blocking in the past that demonstrate the unintended consequences of Internet filtering. For example, in an effort to block access to 31 North Korean sites, ISPs in South Korea also blocked 3,167 unrelated sites hosted on the same servers as the targeted sites. In India, when the Ministry of Communications & Information Technology ordered ISPs to block the Yahoo! Group kynhun, many providers blocked access to the entire domain, resulting in the collateral blocking of thousands of newsgroups. A similar situation occurred when India attempted to block a Hindu extremist Web site and simultaneously blocked at least 8 other unrelated websites. (2)

Methodology & Results

After reports emerged that the Voices for Change site was blocked by Telus, (3) ONI researchers converted the site's domain name ( into its IP address (, which is allocated to AccelerateBiz Inc, located in Miami, Florida. ONI researchers conducted a search for domain names hosted at the same IP address. (4) ONI then checked each of these domain names to ensure that domain resolved to the correct IP address.

On July 27, 2005, ONI volunteers who receive Internet access through Telus attempted to access the Voices for Change website at its domain name ( and at its IP address ( and found both to be blocked. When attempting to access the domain name and IP address, there were no messages indicating that the ISP was blocking the site. Rather, the sites were simply inaccessible, as if they had been taken down or a network error had prevented a connection. Two of our volunteers -- one connecting from the University of Alberta and one connecting from the ISP Interbaun, both of which acquire their Internet access through Telus -- also found the site inaccessible at both the domain and the IP address. It appears that ISP's, for whom Telus is an upstream provider, were also affected by the filtering.

Next, ONI volunteers conducted similar manual requests for a random sample of domain names hosted on the same IP address and found them to be inaccessible also. Since direct requests to the IP address were blocked, only a small sample was required to confirm that all domains hosted on the same IP address were in fact blocked.

Finally to elucidate where the blocking occurred, ONI volunteers also performed traceroute requests for the IP address ( Traceroute is a software tool that allows users to track the route that packets take from their computer along electronic networks to reach the intended destination (such as a Web site). The traceroute results further revealed that requests for the IP address were blocked at Telus's routers.


Telus's blocking of the Voices for Change site generated considerable criticism of the company's actions. (5) According to Telus spokespeople, the ISP was justified in blocking the site because it contained confidential "proprietary information" about Telus, encouraged people to tie up call centre phone lines, and endangered non-union staff by posting pictures of them crossing picket lines. Telus claims that under contractual agreements with its customers, it has the right to block access to certain sites, such as those containing child pornography.

This poses questions as to whether the Canadian Telecommunications Act has been followed to the letter. Section 36 of the Act states that, without the approval of the Canadian Radio-Television and Telecommunications Commission, a "Canadian carrier shall not control the content or influence the meaning or purpose of telecommunications carried by it for the public," and Section 27(2) of the Act prohibits a Canadian carrier, in providing a telecommunications service, from "unjustly discriminat[ing] or giv[ing] an undue or unreasonable preference toward any person, including itself, or subject[ing] any person to an undue or unreasonable disadvantage". (6)

Quite apart from these important legal and ethical considerations, however, the practical effects of Telus's decision to filter are significant. As this case demonstrates, seemingly compartmentalized decisions to block access to Internet content can have drastic unintended consequences, barring Internet users from reaching hundreds of unassociated Web sites. ISPs can unilaterally block access to large swaths of content with the flick of a switch. By collaterally blocking hundreds of completely unrelated sites, Telus has vividly demonstrated the dangers of Internet filtering, particularly when it is conducted in an arbitrary and unaccountable manner.

About the OpenNet Initiative

The OpenNet Initiative is a partnership of the Citizen Lab at the Munk Centre for International Studies, University of Toronto, the Berkman Center for Internet & Society at Harvard Law School, and the Advanced Network Research Group at the Cambridge Security Programme, University of Cambridge.

The OpenNet Initiative releases occasional bulletins based on our ongoing research. These bulletins are meant to be limited, focused responses to current events, policy debates, and/or issues raised by our ongoing research that we feel justify immediate wider circulation. Our more detailed analyses can be found in our major reports.


1. McGinnis, Sorcha. "Website ties cut!". Edmonton Sun. Available at

2. OpenNet Initiative. "Filtering by South Korean Government of Pro-North Korean Websites". Available at

OpenNet Initiative. "Internet Content Filtering in India: Variations in Compliance and Accuracy". Available at

3. "Striking union cries censorship". Canadian Press (CP). Available at

"Telus blocks access to pro-union websites". CBC News. Available at

4. Geist, Michael. "The Telus Blockade and the Law". Available at ?option=com_content&task=view&id=914&Itemid=85&nsub=

5. We were able to collect 766 additional domain names from a databse that resolve to There may be more domain names that resolve to this IP address. In addition, some domain names may map to the same site and some domain names that resolve to the blocked IP address may not be active.

6. Telecommunications Act, R.S.C., ch. 38, §§ 27(2), 36, available at; see also Michael Geist, Telus Breaks ISPs's Cardinal Rule, Toronto Star, Aug. 1, 2005, available at