I assume that your divorce is pending. If that is the case, then yes he can file such a motion. Basically, he is representing to the Court that you will collectively benefit by filing Married Filing Jointly versus Married Filing Separately. For instance, in MFJ you would get a total refund issued on one check to the both of you in the amount of $2,000 and MFS you personally get a check for $3,000, but he would owe $2,000 based on Code differences, then the "marital estate" is benefited by the additional $1,000.00.
Keep in mind the court will be concerned about the "marital estate" until such time you are divorced. If you knowingly did something harmful to the marital estate (filed your return knowing that the end result was going to cost the marital estate more money) then your husband could allege you "dissipated" the marital estate. In that case, you would potentially lose your gain and have to pay part or all of his attorney's fees in presenting the issue.
If you are represented by an attorney, you can agree to file your returns in a manner which will receive the best net result for both of you. You can further condition your agreement that the refund to be received will not be spent until the judge rules on how to properly divide the refund, taking into all of the above factors and any other factor which makes the division equitable or fair.
This response is being provided for information purposes only and does not constitute an attorney client relationship. Furthermore, I am only licensed to practice law in the State of Illinois. While there are oftentimes similarities between States' laws, there can also be large differences. You should not rely on this response as legal advice and are highly encouraged to speak to an attorney licensed in your State for an accurate legal answer.
yes and no. no one can force you to file any particular way. but if you choose to file in a way that costs the marital estate more collectively than it would on a joint return, the court could consider that to be dissipation.
discuss this with your lawyer. if you do not have one, you need one.
You cannot be forced to file a joint return. However, if you file separately and this results in more tax liability for either party, (which is almost always does,) then you might be found to have dissipated marital assets and would be responsible for the loss. You need to discuss this with your attorney and if you do not have one, you should hire one, especially since your spouse is represented.