The unnamed Warner Bros. Pictures film would look at animal trafficking from a number of perspectives, similar to 2000's "Traffic," directed by Steven Soderbergh and written by Stephen Gaghan, The Hollywood Reporter said.
"Traffic," adapted from the British TV series "Traffik," explores the illegal-drug trade from the perspective of a user, an enforcer, a politician and a trafficker, with their stories edited together.
In this case, the story would look at trafficking from different angles including those of the ground war on poachers in the African savannah and how animal material ends up in Paris fashion houses, the newspaper said.
The trio are looking for a screenplay writer, the Reporter said.
English actor Hardy -- who played arch-villain Bane in Christopher Nolan's recent Batman film "The Dark Knight Rises" -- came up with the new film's idea, the Reporter said.
He was inspired by friends who are former Special Forces operatives and later became anti-poacher fighters in South Africa and other countries, the newspaper said.
Maguire -- best known for his role as Peter Parker aka Spider-Man in Sam Raimi's "Spider-Man" film trilogy -- has been good friends with DiCaprio since their early-career days, when they found themselves auditioning for roles opposite each other.
The pair made an informal pact to help each other get parts in their movies, TV shows and other projects.
They both star in the 3D romantic drama "The Great Gatsby," to be released next year.
DiCaprio is longtime animal-rights activist. He donated $1 million to New York's Wildlife Conservation Society in 2010 and joined a so-far-unsuccessful campaign by California's Animal Legal Defense Fund to free a tiger named Tony, who has spent a decade in a roadside cage at the Tiger Truck Stop in Grosse Tete, La.
DiCaprio became the spokesman last year for a campaign organized by the International Fund for Animal Welfare to protect elephants.