"Halle has serious concerns for her daughter's well-being while in the care of her father for any extended period of time and is prepared to take all necessary steps to protect her," the actress's rep tells PEOPLE.
To clear her schedule for custody litigation, Berry, 44, pulled out of the film New Year's Eve, set to start filming this week in New York. She's being replaced by Katherine Heigl.
"She has attempted to resolve these custody issues amicably with her daughter's father, Gabriel Aubry, directly, but given his lack of cooperation, Halle has no choice but to seek swift judicial intervention," her rep says.
Aubrey, 35, filed court papers Dec. 30 seeking to be formally recognized as Nahla's father and to establish that he'll share custody. The couple split last April.
There was no word on what prompted the custody dispute.
Berry's rep says, "Halle has always made the needs and safety of her daughter her first priority and, both while Halle and Gabriel were a couple and since their break-up, Halle has only acted in her daughter's best interest."