An Australian parliamentary committee has expressed concern that legislation to force internet service providers (ISPs) to block sites such as The Pirate Bay could limit freedom of expression.

The Australian government introduced legislation in March that would allow rights holders to get an injunction placed on ISPs to force telcos to block specific overseas piracy websites from access by Australian users.

The rights holders would need to demonstrate that the primary purpose of a website is for the infringement of copyright before the Federal Court will order ISPs to block it.

The legislation has been unsurprisingly welcomed by rights holders -- albeit arguing that the legislation should make it even easier to block sites than is currently contained in the Bill -- but has been condemned by consumer groups and internet companies, including Google.

In a report handed down by the Joint Parliamentary Committee on Human Rights on Wednesday, the committee said that the legislation could result in sites being blocked that are for legitimate purposes, and it would therefore be a breach of the right to freedom of opinion.

Australia doesn't have a Bill of Rights; the rights to freedom of opinion and expression are protected by article 19 in the International Covenant on Civil and Political Rights, the committee stated.

"While a website may have disproportionately high infringement of copyright materials, preventing users who are legally sharing or distributing files from accessing these websites, and preventing the general public from accessing such lawful material, could potentially limit their enjoyment of the right to freedom of opinion and expression, and their right to receive information," the committee stated.

By granting injunctions to block websites, it could lead to smaller content producers who use torrenting websites as a legitimate platform to have access to their content blocked in Australia, the committee stated.

The committee said that in the legislation, the government had not demonstrated that blocking sites is a proportional response to online copyright infringement, and called on the Attorney-General's Department to explain whether the limitation on the right to freedom of expression is proportionate.

The legislation is still being examined by a separate Senate committee, which was due to report on Wednesday. The committee was granted an extension earlier this week, and will now report on May 29.

Australian Human Rights Commissioner Tim Wilson, who the government appointed to focus on freedom of speech issues in particular, told the Senate committee earlier this month that stopping copyright infringement is "consistent with advancing human rights", because property rights "are human rights".

Wilson did, however, state that without a proper fair use exception in Australian copyright law, the legislation could "unreasonably restrict freedom of expression".

The Attorney-General's Department has also revealed that its estimated cost of AU$130,000 per year for ISPs to block infringing sites was based on the UK model, and amounts to an average of 10 injunctions per year for the major ISPs. These 10 injunctions can include more than one website each.

The UK model will differ from the Australian model, however, as ISPs are fighting to ensure that all ISPs are included in the scheme, and, unlike the UK, Australian ISPs do not have as broad-ranging content filters already in place.