This is a tricky question, because the answer will mislead you. The answer is that as to a Federal Return, absolutely not, and as to a California State Return, probably not. So the answer is no, neither you or the judge can make them do that.
But you are asking the wrong question. The question should be what is the way we can send the least amount of tax to the government. Once you, your CPA and your attorneys know that, you need to try to file the return(s) in the way that is most advantageous to both of you. Usually, whatever tax is saved, is split equally in some manner. In most cases the parties agree through the attorneys to just split the return.
If the other side wants to cut off their nose to spite their face (or cut your nose off to spite your face) then try to get that to the court's attention and hope that the court will at least rule in your favor on other issues as a punishment for being ridiculous as to this issue.
For example, you could request in your court documents that the return be filed joint and the return be split. Attach a statement from the CPA explaining the situation. If you are the judge and the other side was not willing to sign a paper that would result in a $4,000 tax return, would you as the judge be inclined to favor one side over the other when it came to the issue of which of the parties has to pay the attorneys? What about the issue of who is telling the truth? Would you give a parent custody who would rather that $4,000 be lost to the family?
Thomas Kendall is a partner in the law firm Kendall & Gkikas, LLP. Since 1994, he has successfully fought for joint share parenting plans for fit parents. During and after the divorce process, Kendall and Gkikas, LLP has the in-depth knowledge it takes to help you make these positive adjustments to satisfy the court and for you to remain a major part of your children's life.
Certified Divorce Financial Analyst
Business Valuators / CPAs