Ninja: American Warrior (1987)
Ninja Commandments (1987)
Ninja Death Squad (1987)
A special agent is sent to stop a ninja squad assassinating military leaders. He manages to make himself invisible and so cause an earthquake.
Ninja Destroyer (1986)
Ninja Dragon (1986)
Ninja Empire (1990)
(aka Ninja Knight, aka Ninja Knight: Thunder Fox)
Ninja Force of Assassins (1988)
This one has gangsters and Interpol and White Ninja vs Black Ninja, though the White Ninja becomes two Blue Ninjas and the 2 guys who become 10 Black Ninjas do not include the original Black Ninja.
Ninja in Action (1987)
Ninja Kill (1987)
Ninja Project Daredevils (1985)
aka Ninja Masters of Death
Ninja Phantom Heroes (1987)
aka Ninja Empire, aka Ninja Knight: Brothers of Blood
Okay, this one involves a guy in a labor camp getting set free if he can take down a crime organization. This one seems to have its fans, but I don't know why.
Ninja: Silent Assassin (1987)
aka Ninja Operation:Knight and Warrior, aka Black Ninja
Ninja: The Battalion (1988)
Ninja the Protector (1986)
aka Project Ninja Daredevils, aka Ninja: The Story
This one has Jackie Chan in a small role, but it's a Richard Harrison flick. This one has two brothers fighting a forger.
Ninja, the Violent Sorcerer (1987)
aka Ninja, the Violent Sorceror
Ninja Thunderbolt (1989)
Ninja USA (1985)
aka Ninja in the USA, aka USA Ninja
Two cops investigate a drug dealer. That drug dealer saved the lives of the two cops when they were kids and he was in the military (back story!) and now he has ninjas in his employ. This one's one of the more entertaining efforts.