The Recording Industry Association of America (RIAA) has insisted that it will only serve lawsuits on what it describes as "substantial" distributors of copyrighted music.

The RIAA has issued 1,075 subpoenas to ISPs in an effort to extract information about alleged illegal file sharing by internet users as it prepares the lawsuits.

But some ISPs have expressed fears they could be turned into 'internet police', and are contesting the subpoenas.

According to Reuters, RIAA president Cary Sherman said in a letter to US Republican senator Norm Coleman: "The RIAA is gathering evidence and preparing lawsuits only against individual computer users who are illegally distributing a substantial amount of copyrighted music."

Senator Coleman is investigating the RIAA campaign and has expressed fears that the trade body is being too heavy-handed in its approach.

The first lawsuits are expected to be filed around the end of this month, or early next month.