Union was born in Omaha, Nebraska, the daughter of Theresa ( Glass), a phone company manager and social worker, and Sylvester E. Union, a military sergeant. She was raised Roman Catholic. During her childhood, she was taught to be "an independent woman, standing on my own two feet, and that's the road I opted to take." According to Union, her mother taught her to have a "world perspective" and took her to a gay pride parade at the age of eight after the family moved to Pleasanton, California, where she attended Foothill High School.