Ex refuses kidz vacationing outside the US

I been divorced for over 4 years, My ex and I have joint custody. I planned a trip with the kids for 2 weeks outside united states, but she refuses to give me the kids passports. She thinks I may stay outside the US with the kids. What should I do. There is any legal action I can take. Thanks

You will need to file an action for child custody and have the court determine whether the passports should be released.