Education and policing are more effective than the filter says the group.
Google and Yahoo have joined two Australian organisations calling for a "rethink" of the country's controversial internet filter plans.
The Australian government has announced proposals to introduce a mandatory filter which would block all RC (Refused Classification) content.
The groups argue that the subjects covered by RC material are too wide-ranging for a blanket ban.
They also warn that the filter will not "effectively protect children".
They claim this is because hardcore material, specifically that featuring children, tends to appear on chatrooms and peer-to-peer networks which are more difficult to filter.
The signatories include the Australian Library and Information Association (ALIA) and the Inspire Foundation, which encourages young people to get online.
ALIA's Executive Director Sue Hutley said that blanket bans on material through filtering have been "shown to trap legitimate information and adversely affect valid internet access and performance".
The statement on the ALIA website adds that a report about government trials of the filter acknowledged the strain of filtering sites with very high traffic.
Dealing with sites such as YouTube could "cause additional load on the filtering infrastructure and subsequent performance bottlenecks," they claim.
Ms Hutley warns that the current filter proposals would create a "false sense of security" for Australian web users.
"We are directing our support for national cybersafety education and increased funding for policing," she said.
The filter, first announced by Stephen Conroy (Australia's Minister for Broadband, Communications and the Digital Economy) in 2008, has proved controversial.
Groups including Systems Administrators Guild of Australia (SAGE-AU) and Electronic Frontiers Australia have spoken out against it, and the topic has trended highly on Twitter.
On 10 and 11 February an activist group called Anonymous attacked several official Australian government websites in protest, taking them offline for short periods of time.