Four record companies have brought a High Court action to compel Eircom - the State's largest broadband service provider - to prevent its networks being used for the illegal downloading of music.
It's the first case to be aimed at the service provider rather than at individual illegal downloaders.
The four record companies taking the action are EMI, Sony BMG, Universal Music and Warner Music.
Willie Kavanagh, Managing Director of EMI Ireland and Chairman of the Irish Recorded Music Association, said because of illegal downloading and other factors, the Irish music industry was experiencing a "dramatic and accelerating decline" in income.
He said sales in the Irish market dropped 30% in the six years up to 2007.
EMI and the other companies are challenging Eircom's refusal to use filtering technology or other measures to voluntarily block or filter illegally downloaded material.
Last October Eircom told the companies it was not in a position to use the filtering software.
Eircom also told the companies that it was not on notice of specific illegal activity which infringed the companies' rights and it had no legal obligation to monitor traffic on its network.