The 66-year-old Fleetwood Mac star has partnered with Talenthouse for a competition that will reward the winner with a cash prize and a professional photo of Nicks wearing the shawl, reported Contactmusic.
The winner and the photo will also be featured on Nicks' website and social media pages.
Announcing the contest, the 'Rhiannon' singer said, "In 1968, a very handsome boy brought me a poncho from South America. I knew it was magic and that someday I would copy it in chiffon or leather or beaded material.
"I realised that wearing a poncho or a long shawl gave me something to work with up on the stage. Big movements, big twirls, you need to be seen from far away. So I made that a big part of my stage clothes. It became totally intertwined in my fashion style."
The competition ends on September 29 and the winner and runner-up will be announced on October 14.