People for the Ethical Treatement of Animals (PETA) have written a statement to the `Walk the Line` star after she was seen with the £2,370 Chloe bag, revealing how the purses are created.
The group said: "No matter how much Reese paid for the bag, the animals paid a much higher price.
"Every year, millions of snakes are impaled on hooks or nailed to trees by their heads and skinned alive. We can`t imagine that she`d wish to contribute to this hidden suffering, especially for something as frivolous as a fashion accessory that can be replicated with no bloodshed."
The group - which in 2006 named Reese one of the world`s sexiest vegetarians - claimed the look was easily made without causing harm.
PETA added: "These days, it`s easy to have a look that kills without killing - with fake snake, mock croc, python pleather, and other designer items that pay tribute to the beauty of these animals without massacring them."
The group have previously targeted celebrities including Paris Hilton, who was pelted with flour during a fashion show in London in 2006 for modelling for Julien Macdonald, a designer who uses fur.