The US record industry is planning to sue people who swap music over the internet.
Record companies believe song-swapping is costing them sales
Starting on Thursday, the Recording Industry Association of America (RIAA) says, it will gather evidence against users of "peer-to-peer" software such as Kazaa, and file $150,000 (£90,000) lawsuits against them.
The RIAA says its sales have been hit hard by the software, which allows users to swap music, films, and other files over the internet.
But the president of one peer-to-peer site blasted the RIAA threat as counter-productive.
"When you start suing all your customers, it's not going to leave a good taste in their mouths," Wayne Rosso, of Grokster, told BBC News Online.
"They're out of their minds," he said.
The RIAA - whose members include AOL Time Warner, Vivendi Universal, Sony, Bertelsmann and EMI -
says it will target the heaviest users of song-swapping services.
Its president, Cary Sherman, said: "We're going to begin taking names and preparing lawsuits
against peer-to-peer network users who are illegally making
available a substantial number of music files to millions of
other computer users."
File-swappers trade an estimated 2.6 billion songs, movies and other files a month, the industry says.
The RIAA expects to file at least several hundred lawsuits
seeking financial damages within eight to 10 weeks.
Kazaa, the most popular software for file sharing,
reported that the number of its users online fell roughly
16 percent by late Thursday morning shortly
after the RIAA announced its new campaign.
The move raises the stakes substantially in the long-running battle over file-swapping.
Most previous lawsuits have targeted websites such as Napster, the industry pioneer that was shut down by legal action.
Record companies have also planted dummy files masquerading as popular tracks to try to deter song-swappers.
A recent court ruling makes it easier to track down copyright violators through their internet providers, and last month four college students agreed to pay damages after being sued by the RIAA.
Mr Sherman said he expected lawsuits asking for damages of $150,000 for each copyright violation to be filed in six to eight weeks.
Computer users who wished to avoid legal action should change the settings
on their software to block access to their hard drives, or uninstall the software completely, Mr Sherman said.
The organisation hit a snag last month when a judge ruled two networks, Grokster and Morpheus, should not be shut down because they do not control what is traded on their systems.
Grokster's Mr Rosso says that court loss is the reason the RIAA has turned its attention to individuals.
"They're upset that we beat them in court," he told BBC News Online.
Supporters of song-swap networks say they are an easy way for music fans to discover new artists - but record companies liken the practice to shoplifting.
Mr Rosso says there are many ways to make money from file-swapping.
"Licence it, sell waivers to downloaders, tax CD burners, tax software-ripping programmes," he said.
He said Grokster would be happy to sell licenses to download music, but that none of the record companies would discuss it with his firm.
And he said Grokster would resist the RIAA's latest move.
"We're going to fight back using every means at our disposal," he said.