Canadian cable and telecom giant Rogers Communications has come under fire for violating Internet neutrality principles after testing a new technology called Internet Subscriber Notification System (ISNS) that inserts messages – like ads – on third-party websites. People for Internet Responsibility co-founder Lauren Weinstein blogged about the incident in which Rogers spliced a Yahoo-branded customer service message onto the Google (NSDQ: GOOG) homepage. Last month, of course, Rogers and Yahoo (NSDQ: YHOO) expanded their access deal to a revenue sharing one.

Weinstein asks the question in his blog, “Will Web service providers such as Google and many others, who have spent vast resources in both talent and treasure creating and maintaining their services’ appearances and quality, be willing to stand still while any ISP intercepts and modifies their traffic in such a manner?”

Meanwhile, Rogers has defended its practice of posting these messages, comparing it to mobile providers sending its subscribers messages when they are about to exceed their monthly airtime allowances. A Rogers spokesperson told Toronto Star, “We’ve done customer research on the technology and the feedback was good. So now we’re trialling it.”

Google, on the other hand, has expressed its annoyance for the situation, saying, “As a general principle, we believe that maintaining the Internet as a neutral platform means that carriers shouldn’t be able to interfere with Web content without users’ permission,” the Google statement said. “We are in the process of contacting the relevant parties to bring this to a quick resolution.”