One other thing to point out is that the father can put anything on his tax return that he wants, but it doesn't make it right. If he tries to claim the child as a dependent and someone else also claims the child, the IRS will send letters to start an investigation. Each person who claimed the child will be asked to prove they meet the conditions of claiming a dependent--such as that the child lives with them, etc. You can't stop the father from trying to claim the child (and starting an investigation), but as already described, the father does not have legal standing to claim the child unless the mother voluntarily allows it, which must be done in writing. Even then, certain special rules apply.
