Union appeared in the 2000 film Love & Basketball. In the same year, she performed the role of Isis in the cheerleading movie Bring It On, opposite Kirsten Dunst. Bring It On helped push Union into the mainstream. Union has said that of all her films, Bring It On gave her the "biggest boost". It led to Union being cast in the CBS television drama City of Angels as Dr. Courtney Ellis. Union was featured in The Brothers and was seen as having a "beguiling sincerity, even when she's fudging the truth. " Union was cast in her first leading role in the 2003 film Deliver Us from Eva with LL Cool J. This was her second time working with the rapper since making a cameo in his video "Paradise" in 2002. When casting Eva, director Gary Hardwick was looking for an actress capable of instantly changing "from funny to caustic and dramatic. " Hardwick had previously worked with Union in The Brothers and believed she was perfect for the role of Eva. Union's role in the film was met by praise, with Dustin Putman of All-Reviews. com wrote that she was "the star attraction, and the number-one reason to even consider seeing the film. " Union drew influence from her father for the "stern" look she had in the film, admitting that she had stolen it from him.