I have physical custody of my children through my divorce decree but my exspouse has claimed on of the children on her taxes even though she pays no child support (even though I have an Attorny General Case against her) and the children lived with me the entire year last year. What steps can I take to stop this?

Inform your ex that you are going to take the deduction on your taxes this year as is your right to do so. Also, tell her that if she also takes the deduction you will both get audited by the IRS and it will be found that you are legally entitled to the deduction. Therefore she will have to payback the money she wrongfully deducted plus interest and penalties.

If she doesn't believe you ask her to go check this with her accountant or tax preparer and they will say exactly what I just said.

If I follow you, your ex has already filed her return so Cody's advice is too late.

So you need to file your return and include proof that you are entitled to the deduction. When the IRS checks the returns, they will see that she was not entitled to claim them and go after her.