"Actor & bestselling author @aliciasilverstone would rather go naked than wear wool!" the organization captioned the stunning new photo of the actress. "Sheep are gentle, kind animals who are often beaten, kicked, & mutilated so their wool can be made into sweaters, scarves, & other clothing items. Choose fake, for animals' sake!"
Alicia Silverstone through the years
Alicia Silverstone through the years
LOS ANGELES, CA - NOVEMBER 24: Actress Alicia Silverstone attends the 2013 American Music Awards at Nokia Theatre L.A. Live on November 24, 2013 in Los Angeles, California. (Photo by Jason Merritt/Getty Images)
NEW YORK, NY - NOVEMBER 14: Actress Alicia Silverstone attends the after party for the opening night of 'The Performers' on Broadway at Espace on November 14, 2012 in New York City. (Photo by Stephen Lovekin/Getty Images)
SANTA MONICA, CA - NOVEMBER 07: Actress Alicia Silverstone arrives at the Weinstein Company & Dimension Films' American Film Market cocktail party on November 7, 2010 in Santa Monica, California. (Photo by Amanda Edwards/Getty Images)
LONDON - JULY 17: Actress Alicia Silverstone arrives at the UK premiere of 'Stormbreaker' held at the Vue Cinema in Leicester Square on July 17, 2006 in London, England. (Photo by MJ Kim/Getty Images)
HOLLYWOOD - JUNE 16: Actress Alicia Silverstone attends the Hollywood Reporter's 35th annual Key Art Awards at the Kodak Theatre on June 16, 2006 in Hollywood, California. (Photo by David Livingston/Getty Images)
LOS ANGELES - DECEMBER 4: Actress Alicia Silverstone arrives at Hollywood Life Magazine's Breakthrough of the Year Awards at the Music Box at the Fonda Theatre on December 4, 2005 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)
WASHINGTON D.C. - APRIL 16: Alicia Silverstone poses for photos before the Art of Compassion Gala sponsored by the Physicians Committee for Responsible Medicine (PCRM) on April 16, 2005 in Washington, D.C.. PCRM promotes good nutrition and alternatives to animal research. (Photo by Stephen Boitano/Getty Images)
LOS ANGELES - MARCH 24: Actress Alicia Silverstone arrives at the premiere of MGM's 'Beauty Shop' at the National Theater on March 24, 2005 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)
BEVERLY HILLS, CA - MARCH 20: Actress Alicia Silverstone attends The 18th Annual Genesis Awards on March 20, 2004 at the Beverly Hilton Hotel, in Beverly Hills, California. (Photo by Giulio Marcocchi/Getty Images)
BEVERLY HILLS, CA - JANUARY 25: Actress Alicia Silverstone attends the 61st Annual Golden Globe Awards at the Beverly Hilton Hotel on January 25, 2004 in Beverly Hills, California. (Photo by Carlo Allegri/Getty Images)
LOS ANGELES - NOVEMBER 11: Actress Alicia Silverstone attends the special screening of 'Die Another Day' on November 11, 2002 in Los Angeles, California. The film opens in theaters nationwide on November 22, 2002. (Photo by Robert Mora/Getty Images)
NEW YORK - JUNE 9: Actress Alicia Silverstone arrives at the third annual Directors Guild of America Awards June 9, 2002 in New York City. (Photo by Getty Images)
LOS ANGELES, UNITED STATES: US actress Alicia Silverstone, wearing a Vera Wang dress, arrives 25 March at the 68th Annual Academy Awards in Los Angeles, California. AFP PHOTO Vince BUCCI/mn (Photo credit should read Vince Bucci/AFP/Getty Images)
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The ad, which was revealed on Instagram, shows theClueless icon posing naked while holding a sheep mask, in an over-the-shoulder shot taken in a beautiful forest.
"Wear your own skin. Let animals keep theirs," reads the ad.
Silverstone shared why she stripped down for PETA in a video on the organization's website.
"They're cut. They're harmed," she says about sheep. "They get very seriously wounded, and there's no care for them when they're wounded. It's just move on to the next. These are not creatures to the people who are doing this. They're just objects. When the sheep are no longer useful, they're killed. So there is no happy place they get to go for being a wool sheep."
An avid animal rights activist, Silverstone dedicates a section of her website to "Animal Life."
The actress' new campaign comes nine years after she first stripped down for PETA, in a 2007 ad promoting vegetarianism. Actress Eva Mendes and former Playboy Bunny Holly Madison also did nude campaigns for the organization that year.
Supermodel Christy Turlington first posed in the buff for the charity's anti-fur campaign in 1993, while Pamela Anderson made waves with her 2003 shoot, in which she wore nothing but a lettuce bikini.