"Our primary concern is that the scope of content to be filtered is too wide," a Google representative told the Sydney Morning Herald, the same week Google ceased censoring its content in China.
"Some limits, like child pornography, are obvious. No Australian wants that to be available -- and we agree," the company added. "But moving to a mandatory ISP level filtering regime with a scope that goes well beyond such material is heavy-handed and can raise genuine questions about restrictions on access to information."
Yahoo sounded a similar note on Tuesday, expressing concern that the restrictions imposed this year could grow in number and magnitude, creating a regime of Web censorship.
"Clearly some of this content is controversial and, depending on one's political beliefs, rather offensive," a Yahoo spokesman told the newspaper. "However, we maintain that there is enormous value in this content being available to encourage debate and inform opinion."
Google and Yahoo -- as well as other opponents to the deal, including Microsoft -- are clear stakeholders in the debate. They could perhaps find themselves liable if banned content becomes available on their websites or online services.
It is a struggle that Google, at least, already knows all too well: A dispute with Italian authorities over questionable video content resulted in jail sentences for four company executives, who an Italian judge said did not take down the questionable clip fast enough.
And it was only on Monday that Google announced the end of its self-censorship practices in China, despite threats of retaliation by Beijing. The search company's new site -- which redirected Chinese users on Monday to Google's Hong Kong page -- has since been blocked by Chinese censors.
However, Google signaled Tuesday it might "not be technologically possible" to police sites like YouTube, Twitter, Facebook and news and image search results in the way the Australian government wants.