He should try to get his ex to agree to modify visitation to provide for a halfway meeting point or else he should go to court and prevent move.
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I don't think you'll need to go nuclear, yet. Honestly, this is a common situation. A letter from an attorney informing her that court action will be taken if she moves should be sufficient to get her to agree to 50/50 travel.
Taking this approach before filing keeps relations cooler, is more cost effective, and faster. Naturally if this fails, I would argue that'll you'll need to bring this to the court's attention vis a vis a petition.