Proposed changes to copyright law would mirror Labor's dumped internet filter and would not curb online piracy, the free market think tank the Institute of Public Affairs has said.

The IPA has slammed ideas raised in the government's discussion paper and warned there is a "real risk" Attorney General George Brandis will push ahead with the proposals "in defiance of Liberal values".

Illustration: Michael Mucci

The government is calling for debate about an idea to introduce a new special injunction that would force Australian internet service providers to block sites which enable illegal downloads of content such as films or television shows.