Taxpayer groups hit out at Perth and Kinross Council who were forced to reveal the payment following a nine-month disclosure battle.
The Mysterious Girl singer made a 30-minute appearance, and council bosses claimed the release of payment details would be a “breach of confidence”.
But the local authority was forced to give up the figure after a ruling by the Scottish Information Commissioner.
Andre’s backing band, Jack Pack, received a further £4,000 and disco stars Boney M were also paid £8,000 to play at Perth’s Christmas party in November.
The council spent an additional £4,500 on travel, accommodation, and other expenses.
Jonathan Isaby, Chief Executive for the Taxpayers Alliance, condemned the spending as a “vanity project” by the council.
He said: “What a mysterious decision. Taxpayers will wonder what councils think they’re doing when they’re trying to make necessary savings whilst protecting frontline services.
“There is simply no excuse for such extraordinary spending on vanity projects. Those responsible for this decision must be held accountable.”
Perth councillor John Flynn, slammed the £20,000 fee as “extortionate”.
He added: “We are elected members but we don’t get a say on who performs and how much they get paid.
“I don’t think councillors would have voted for this.”
A spokesman for Perth and Kinross Council said the release of the payment details “seriously jeopardises our ability to secure headline acts for future events.”
He said: “Following an order from the Scottish Information Commissioner, the council is releasing the fees paid to artists for the 2014 Perth Christmas lights switch on.
“Revealing these fees seriously jeopardises our ability to secure headline acts for future events and indeed, we have already received correspondence from the entertainment industry to this effect.”
The council’s infrastructure committee convener, John Kellas, said the event had been a great success and claimed it added £1.9 million to the local economy.
He said: “The festival programme is still a fairly new concept to Perth, but year-on-year the event has got bigger and better and we are learning from each one.
“It is disappointing that we are having to release these figures and the potential impact this will have in the council being able to secure a high-profile, popular celebrity personality for future events is a concern to the continued success of the Winter Festival.”