Louisiana is a community property state - Community property states. If you live in Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, or Wisconsin and file separately, your income may be considered separate income or community income for income tax purposes.
See Pub 555 for information
<a rel="nofollow" target="_blank" href="http://www.irs.gov/publications/p555/index.html">http://www.irs.gov/publications/p555/index.html</a>
Are you sure that he took a distribution (which is taxable), and not a loan (which is not taxable ) unless he defaults on repayment?
married couples always have the choice of filing jointly or separately. However, separate filing can significantly increase your tax bill or reduce your refund because some deductions phase out earlier and some deductions and credits are disallowed entirely. (It can be especially bad if you have child dependents.) The biggest mistake people make is that when you file separately, both must itemize deductions or both must take the standard deduction, even if there aren't enough itemized deductions to go around. You can't load all the itemized deductions on one spouse and have the other spouse take the standard.
Either way, the marriage considered as a unit will pay about $4000 tax on the 401K withdrawal, filing separately might result in even more tax owed due to the loss of deductions. You will have to figure it both ways and then decide.
As an aside, many 401(k) plans (e.g., in Community Property States) require the spouse's signature before a distribution or loan can be taken.
You can still file jointly. But, include an Injured Spouse Allocation Form 8379 with your return.
Form 8379 would only apply if there was a past-due tax debt owed only by one spouse. That doesn't seem to be the case here.
I agree. Even if the spouse's signature was required, but not obtained, that is a legal (not income tax) matter.
However, if they live in a community property state and file separately, depending on state laws, 1/2 of the 401(k) income could be subject to income allocation on each spouses separate return. Since community property laws are different in every state, in complex situations such as this which involves retirement accounts, I usually suggest seeking professional help from a tax professional (not store-front) that deals with community property.
I don't know it that applies or not since we don;t know the state where the OP lives, but if it is a community property state then filing separately could result is a much higher tax.