The UK Court of Appeal will decide tomorrow whether online message board postings can be considered libellous.
If the 2008 ruling in the case of Nigel Smith v ADVFN Plc and others is overturned, the decision will set a precedent under which UK internet users could be prosecuted for comments posted online.
Smith began a lawsuit two years ago against ADVFN Plc, which operates a financial online bulletin board, because the board contained an alleged 150 defamatory comments about Smith.
Many of those who posted the comments used pseudonyms or 'avatars' to hide their identity, and Smith argued that internet service providers should be ordered to disclose their IP addresses.
However, the judge on the case, Justice Eady, ruled in favour of freedom of expression on the internet.
Eady said that the postings should be considered slanderous rather than libellous for a number of reasons, including the fact that the comments were read by a small group of people who all shared a similar interest, and were made as part of a casual conversation similar to "people chatting in a bar".
Smith's initial appeal against Justice Eady's verdict was refused, but was then granted on 30 July 2008.
The hearing will take place tomorrow.
Facebook database included text-message metadata - despite not using Facebook Messenger for SMS
Successful attack could result in harm to patients and financial loss, warns NHS governing body