The International Federation of Library Associations and Institutions (IFLA) has publically objected to the UK's Digital Economy Act (DEA).
The DEA, which was passed just before the dissolution of the last parliament, says ISPs should restrict access to web sites that infringe copyright laws through P2P file sharing.
A letter from the IFLA's senior adviser, Stuart Hamilton, which was posted on a digital rights blog called Slightly Right of Centre, explains how this part of the act could see libraries incur significant financial obligations.
He also says that libraries fall into a grey area because they could be seen as both subscribers and providers of internet services:
"As an ISP, a library can be made responsible for the monitoring of their networks for copyright infringement and incur significant financial obligations as a result. As a subscriber, libraries are likely to receive notifications from their ISP to the effect that a copyright owner has made a report against them for alleged copyright infringement.
"The financial and time costs of complying with or appealing against this type of situation cannot be underestimated, nor can the types of penalty that could be imposed on libraries as result of an infringement by an individual user."
Hamilton also emphasises that these unknown costs are compounded by the fact that library budgets are being cut across the UK and Europe.
He also argues that a library-goer's freedom to access information must be protected.
"The chilling effect of the monitoring of internet use should not be underestimated, and the electronic recording of library users' information-seeking activities is not consistent with a democratic approach to access to knowledge," he writes.
Following the passage of the DEA, it came in for huge criticism from ISPs who will be held liable for users accessing restricted sites.
This criticism comes shortly after the government ordered communications regulator Ofcom to review the DEA, which is also likely to cause delay to its implementation.
Culture Secretary Jeremy Hunt said that although he had "no problem" with the principle of the DEA, the review from Ofcom is necessary as "it is not clear whether the site-blocking provisions in the act could work in practice".
The IFLA represents 750,000 library professionals in more than 150 countries.