The trio of famous faces have agreed to lend their likenesses to the collection which has been organized by People for the Ethical Treatment of Animals (PETA) and will be released in the US on Tuesday.
Lisa Lange, vice president of the animal rights organisation, said: "These are very influential people, and not everyone knows that these folks are vegetarian."
Other celebrities to feature on the stamps include Woody Harrelson, Chrissie Hynde, Pamela Anderson, Morrissey, Joan Jett, Bryan Adams, 'Jackass' star Steve-O and Leona Lewis.
Lange believes the special edition stamps will highlight the true plight of animals in slaughterhouses and hopefully convince more people to give up eating meat.
She added: "It’s just another way to be able to talk about what animals go through in slaughterhouses."
The postage payment mark series also includes statements from the stars revealing why they decided to become vegetarians or why they eating plan is important to them.
Academy Award-winner Portman stated: "Eating for me is how you proclaim your beliefs three times a day."
The stamps can be purchased throughout December at www.PETA.org.