In a letter to Gov. Luis Fortuno, the Puerto Rico-born actor says the Mauritius-based company Bioculture's facility would be cruel. It would supply monkeys to pharmaceutical companies for research.
Fortuno's office and Bioculture did not immediately return calls seeking comment Thursday.
Bioculture community coordinator Jacinto Rivera Solivan previously said the Guayama facility would be run humanely.
Del Toro won a supporting actor Oscar for his role in "Traffic" and starred in last year's "Che," a biopic of Latin American revolutionary Ernesto "Che" Guevara.