Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Clark v. Commissioner, 40 B.T.A. 333, 335 was an important early United States income tax case. The taxpayers, husband and wife, made an irrevocable election to file a joint federal income tax return rather than separate returns on the advice of their return preparer. Subsequently, the Service examined the return and assessed a deficiency against the taxpayers. The deficiency existed because the return preparer took a larger deduction from income for capital losses than was allowed by law.