Alicia Silverstone goes naked for PETA to end sheep cruelty -- see the stunning pic!

"Choose fake, for animals' sake!"

That's the message behind Alicia Silverstone's sexy new nude campaign for animal rights organization PETA.

The 40-year-old vegan shows off her amazing body by stripping completely naked for the nonprofit's latest ad.

NEWS: Pink Gets Naked for PETA

"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!"

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."

WATCH: Alicia Silverstone and Liv Tyler Have a 'Crazy' Reunion

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.

Many celebs have since gone naked for the organization, including Taraji P. Henson, Pink, Khloe Kardashian and Olivia Munn.

See Silverstone reuniting with Liv Tyler, her co-star in Aerosmith's "Crazy" video, below.