I claimed my son due to arrearages. My ex is suing me for claiming him to the tune of 4000 which is less than what he owes. What are my options.

Under federal law, the custodial parent claims the child tax dependency exemption, unless waived by the custodial parent or as ordered by the court. In addition, the custodial parent must  sign IRS waiver form 8332 in the year where the non custodial parent claims the child. Whether arrears are owed or not, is irrelevant to the question of entitlement to claim the exemption, unless there is something spelled out in your court papers that the non custodial parent can’t claim the exemption, where it is allocated to them, if there are any arrears of was record . If your ex served you with a contempt motion and you have claimed the exemption improperly, they may order you to amend your return without claiming the child, which would remedy the situation with her filing an amended return as well claiming the child or the court could order you to pay whatever tax loss she can prove by the difference of claiming the child as opposed to not claiming the child. Effective 1/1/18, for your information, under the new tax reform act, all personal exemptions have been eliminated, including the child tax dependency exemption. The child tax card credit has been increased from $1,000 to $2,000.