My friend's daughter was like this for a long time. Her mom stayed at home with her, and when her dad came home from work, she'd say to him, "No, Dad! Go back to work!"
She is much better now, but I think a lot of it is because she goes to preschool now and her mom has gone back to school. So her dad isn't really seen as the primary interloper between her and her mom.
My son has definitely gone in phases where he prefers one parent to another. He is in extreme mommy mode right now. I have heard him tell his dad, "I love Mommy more than I love you." I've told our son that I really love that he loves me and that it's even ok if he loves me more. But I told him that he must always be kind and polite to his father and to treat him with respect. And telling his dad that he doesn't love him as much as he loves me isn't kind OR polite.
I assume that you are still with your daughter's father? My husband and I are separated, and it definitely is a challenge to make sure that I am not projecting something out there that makes my son feel like I condone unkind behavior to his father. I guess I'd say that you should try to be aware of anything that you may be saying or doing that would make your daughter feel that that sort of behavior is acceptable or effective.