The casting of Zach McGowan as Hawaiian war hero Benehakaka "Ben" Kanahele has caused outrage online, reigniting Hollywood's "whitewashing" controversy.
Ni'ihau will depict a 1941 incident in which Hawaiian native Kanahele, by killing a Japanese soldier, was credited with helping prevent the takeover of an island.
McGowan, of Dracula Untold and Black Sails, looks starkly different from the person he is portraying, which is not going down well online.
"By accepting this role, you support whitewashing. Don't ever deny it and don't cry when it bombs because of boycotting. You're on the wrong side," one Twitter user replied to McGowan, after he tweeted he was "excited" about the film.
The Ni'ihau incident is said to have been a major influence on the US government's controversial imprisonment of Japanese-born citizens in internment camps - a point that has also been referenced on social media over McGowan's casting.
McGowan hasn't responded to the controversy, but has sent tweets of thanks to supporters.
Newshub.