The artists made the decision following a three-hour debate in London in the aftermath of comments from the Featured Artists Coalition (FAC) and Lily Allen.
A joint statement read: "We the undersigned wish to express our support for Lily Allen in her campaign to alert music lovers to the threat that illegal downloading presents to our industry and to condemn the vitriol that has been directed at her in recent days.
"Our meeting also voted overwhelmingly to support a three-strike sanction on those who persistently download illegal files, sanctions to consist of a warning letter, a stronger warning letter and a final sanction of the restriction of the infringer's bandwidth to a level which would render file-sharing of media files impractical while leaving basic email and web access functional."
The release was signed by FAC members Billy Bragg, Radiohead's Ed O'Brien, Sandie Shaw and others, as well as Allen herself.
Allen attended the meeting, despite her earlier claims that she would stay away to avoid her presence detracting from the issues.
O'Brien described her as "extremely brave", adding: "She's taken a lot of flak for what she's said. What she's done has been brilliant because she started the process where artists have stood up and said, you know what, there is a consequence to illegal file-sharing.
"In the meeting, we didn't always agree but we came to an agreement that we thought was good for everyone. We're going to have further meetings like this, we're going to get together - we've realised the importance of doing this together."