The IRS will generally contact the second to file. The first time the SSN is used, it will not be questioned. The second person to file will trigger an alert because they are using a SSN that has already been claimed as a dependent.
Just be ready if they contact you.The language of the divorce decree or child custody agreement is very persuasive. Mail from the child's school which is addressed to the parent is very convincing. If a parent clearly lives in the district where the child attends school, this is also hard for the non-custodial parent to overcome. These are the types of indicia that prove the child lives with one parent for a greater portion of the year. You will probably think of some yourself. Just be prepared to send copies to the IRS if they ask.
Since your child lives with you, you are the custodial parent. You are correct that he would need a Form 8332 release from you to take the deduction. If he claims the deduction too the IRS will send you both a letter asking why you should receive the deduction. Explain the situation to them and you should prevail.
Any individual seeking legal advice for their own situation should retain their own legal counsel as this response provides information that is general in nature and not specific to any person's unique situation. Circular 230 Disclaimer - Advice given in this response cannot be used to eliminate penalties with the IRS or any other governmental agency.
I agree with my colleagues on this matter. This is not an uncommon event. Divorce often creates tension regarding the children as deductions. If there is a problem, you should contact your divorce lawyer and address this matter in court. It is ALWAYS best to have a custodial agreement that does not leave important matters unanswered.
Agreed with all answers. It appears you are entitled to claim the benefit and a Form 8332 would be advantageous. But, some other non-tax factors to consider are your relationship with the father & your incomes. Sometimes the couples work it out so that the person who gets the most benefit claims the child and the taxpayers split the refund in some agreed way.