Can an attorney in a civil matter demand information like tax documents?

It is unclear whether no lawsuit has yet been filed, if you are still in litigation, or whether there has already been a litigation which resulted in a judgment against you.  If you have not yet been sued, and have no agreement obligating you to show your tax returns to the other side, you have no obligation to do so.  Of course, it may be that the attorney is demanding your tax returns because his client won't sue you if you can demonstrate that you don't have significant financial resouces, in which case refusing the demand can result in you getting sued. If you are in litigation, litigants are entitled to see the other side's documents that are relevant to the case.  However, even if the tax returns would be relevant, they are usually (but not always) protected from discovery.  Other financial information, however, again assuming it is relevant, is usually fair game. If a judgment has been entered against you and has not been paid, the judgment creditor is entitled to get discovery about your financial situation in an attempt to locate assets which can be used to satisfy the judgment.  In this context, you may be required to produce your tax records.