Commentary during the development of FASB Interpretation no. 48 suggests the interpretation could be costly for firms because new disclosure requirements could be used by the IRS to more effectively challenge uncertain tax positions. Stock returns around FIN 48 pronouncements suggest investors were not concerned about an increase in tax costs, and investors responded favorably to initial disclosures required under FIN 48. However, we document a significant negative market reaction to subsequent news of a Senate inquiry into these disclosures consistent with investors revising their beliefs over the potential for additional tax costs.

Increasing the conformity between accounting earnings and taxable income has been proposed to improve financial reporting and curtail aggressive tax planning. We find, however, that increasing conformity results in earnings that are less informative. Our inquiry exploits a unique sample of firms forced to change from the cash method to the accrual method for tax purposes, thereby increasing their book-tax conformity. We find that these firms experienced a decrease in earnings informativeness compared to control firms unaffected by the change. To our knowledge, this is the first evidence of tax law changes affecting the informativeness of accounting earnings.