@JBA7
It sounds like you now know the rules better than the ex. If the ex claimed one child in the past without using form 8332, the only way that would go through the system is if the custodial parent had removed the child completely from their tax return. That in turn might have deprived the custodial parent of some tax benefits, although the effect would be less severe if the custodial parent had another child to claim. And if those tax returns are more than three years old, there is no way to go back and fix them.
Yes, the domestic relations court can order the custodial parent to sign a form 8332 for one year or indefinitely. Whether or not the custodial parent has a convincing argument that the court should not do that would have to be determined by proper legal representation.
Form 8332 can only be used to transfer the child tax credit until the child turns 18. After the child turns 18, the exemption can’t be transferred and where the child is a dependent is determined solely on the normal rules of custody and support. So you need to weigh the cost of legal representation now against $2000 per year until the child turns 18 (however old they are now), and also factor in how badly you want to fight for a matter of principle. The other parent has to consider the cost of their legal representation against the $2000 per year they would gain. If the other parent is faithfully paying their child support obligation, one compromise that comes to mind is an offer to simply reduce the child support by $1000 per year or to rebate $1000 per year, which splits the difference and saves a court fight. But I am not an attorney.
