Mr Keiser said he did not just want to shut websites and impose fines, saying if authorities can "throw in some jail time I think we'll be a little more effective".

Bitter battles

The move comes after several years of bitter legal battles against unauthorised services allowing users to download recordings for free.

Publishing companies have taken action against websites in the past, but this will be the first co-ordinated legal campaign by the MPA.

The MPA would target "very big sites that people would think are legitimate and very, very popular", Mr Keiser said.

"The Xerox machine was the big usurper of our potential income," he said. "But now the internet is taking more of a bite out of sheet music and printed music sales so we're taking a more proactive stance."

David Israelite, president of the National Music Publishers' Association, added his concerns.

"Unauthorised use of lyrics and tablature deprives the songwriter of the ability to make a living, and is no different than stealing," he said.

"Music publishers and songwriters will consider all tools under the law to stop this illegal behaviour."

The campaign comes after lyric-finding software PearLyrics was forced off the internet by a leading music publishing company, Warner Chappell.

'No alternative'

PearLyrics worked with Apple's iTunes, searching the internet to find lyrics for songs in a user's collection.

"I just don't see why PearLyrics should infringe the copyright of Warner Chappell because all I'm doing is searching publicly-available websites," PearLyrics developer Walter Ritter said.

"It would be different if they had an alternative service that also provided lyrics online and also integrated [with iTunes] like PearLyrics did.

"But they don't offer anything like that at all."

Warner Chappell were unavailable for comment.