'Help the world'
Billie, who recently slammed the meat and dairy industries for 'torturing animals' to her 26.8 million followers, said: "I just wanted to say happy birthday to Meat Free Monday.
"I've been vegetarian my whole life, vegan for five years. Help the world - I try."
Bloom said: "Happy Birthday, Meat Free Monday. As somebody who loves animals, well all beings really, I think generations to come are gonna look at us and go 'can you believe they used to eat meat? That's crazy'.
"Anyway, we're all doing our very best. Happy tenth birthday you meat-free lovers."
'A compassionate step'
Meat Free Monday, a not-for-profit campaign, aims to 'raise awareness of the detrimental environmental impact of animal agriculture and industrial fishing'.
"Billions of animals are farmed and killed for meat each year... All farmed animals end their lives with a brutal death at the slaughterhouse. Eating less meat is a compassionate step that helps prevent cruelty and suffering," its website states.