The websites and social media accounts of 24 festivals including T in the Park, Bestival, Belladrum Tartan Heart, and Glasgow Summer Sessions will go dark for a day from 9am.
Music fans visiting the homepages of the participating festivals will be met with a completely black window except for a grey light bulb and the message: "Don't be in the Dark about Legal Highs".
Blackout organiser the Association of Independent Festivals (AIF) said its members had banned the sale of legal highs by traders onsite at their events.
It comes after Home Office minister Norman Baker warned authorities are involved in a "race with chemists" in India and China who are producing potentially dangerous new legal highs on a weekly basis.
AIF's co-founder and vice-chairman, Ben Turner, said, "Legal highs are a serious concern for any festival organiser and the issue is only going to get bigger.
"The substances have managed to fly under the radar purely by evolving faster than the monitoring bodies can regulate.
"Banning it at our festivals is only part of the battle however, we need to make fans aware of the dangers of legal highs and help them make safer choices when having fun on-site."
AIF said festivals backing the "blackout" have a combined capacity of more than half a million people and an online reach well into the millions. It hopes to make the "blackout" an annual event."