The 'Empire State of Mind' singer has offered support for Coalition Against Trafficking in Women (CATW), who plan to protest sex advertisements outside the New York City offices of newspaper The Village Voice on Wednesday.
Keys and CATW claim that some classified ads in the paper and on its Backpage webpage have been used to promote prostitution.
Posting on Twitter, Keys wrote: "What if these were your daughters? SO CRAZY! Please stand up with CATW against sex trafficking on Nov 16 in NY."
The Coalition Against Trafficking in Women has opposed sex trafficking and prostitution all around the world since its launch in 1988.
In October, Keys's charity Keep A Child Alive held a benefit gala in New York to honour the life and work of late Beatle George Harrison.
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