The case, filed in response to the NLA's licensing scheme for the supply and receipt of URLs, is expected to take between nine and 12 months to be resolved.
PRCA director general Francis Ingham said: ‘In the face of their aggression, it's not good enough just to talk tough with the NLA - we need to act tough too. That is why we have intervened in support of Meltwater.'
He added: ‘We will now pursue this case with vigour and to a conclusion. We are clear that the NLA's pretensions have no basis in law, and represent an intolerable attempt to restrict and to tax knowledge. We are certain that standing up to the NLA, and standing up for the PR industry, is the right thing to do.'
The NLA caused anger among the PR industry when it announced plans last year to seek payment for paid-for web articles.
In December, the NLA controversially struck a deal with all but two press cuttings agencies and web aggregators for the licensing of paid-for business-to-business monitoring of web content.
While the new web licences came into force on 1 January 2010, the NLA announced it was suspending invoicing until the outcome of the Copyright Tribunal brought by Meltwater News.
An NLA spokesman said: ‘This move from the PRCA comes as no surprise and makes no difference to web licensing for newspaper content. Monitoring agencies are still required to have and pay for a web licence but we will not invoice their clients for their NLA web licences until the Copyright Tribunal has ruled. We regret that, unlike other trade organisations and companies, the PRCA chose not to engage constructively while the NLA consulted on its web licences throughout 2009.'
The Financial Times announced last week that it was was planning to make changes to the way it sells licences for its products. The newspaper is extending its direct licence to include digital images of FT newspaper articles, which are currently licensed by the NLA.