Officers responded to a report of a male bleeding on Railroad Avenue near Westgard Street at about 7:15 a.m. When they arrived they found a man with multiple gunshot wounds.
Emergency medical personnel responded and pronounced the victim dead.
The man was discovered by a dog walker who called 911. A neighborhood check revealed that two residents heard gunshots between 5 a.m. and 5:45 a.m., according to police.
The man's identity has not been released. Police say he is between 18 and 20 years old.
This was Union City's second homicide this year.
Anyone with information about this homicide is asked to call Detective Stan Rodrigues at (510) 471-1365.