A London council plans to launch a voluntary "mansion tax" on high-value properties.
The tax would be for owners of properties worth more than £10m, Westminster Council says.
Nickie Aiken, leader of the council, said she was confident people would pay the optional charge.
"This scheme might have its cynics, but I have spoken to very wealthy people who want to help the borough more," she said.
She explained proceeds could be used to freeze council tax for other council tax payers.
The tax would collect a voluntary supplement of £1,376 a year from the estimated 2,000 owners of £10m-plus properties within band H, doubling what they already pay in council tax.
The scheme would raise an extra £2.75m a year if they all made the payment.
It will come into force from next April and the voluntary contribution will be collectable alongside ordinary council tax.