26 C.F.R. § 1.547-7
The deduction for deficiency dividends, in computing personal holding company tax for any taxable year, is allowable only with respect to determinations under section 547(c) made after November 14, 1954 (the date falling 90 days after the date of enactment of the Internal Revenue Code of 1954). If the taxable year with respect to which the deficiency is asserted began before January 1, 1954, the deficiency dividends deduction shall include only the amounts which would have been includible in the computation of the basic surtax credit for such taxable year under the Internal Revenue Code of 1939. Section 547(g), relating to the denial of a deficiency dividends deduction if the determination contains a finding that any part of the deficiency is due to fraud, etc., shall apply only if the taxable year with respect to which the deficiency is asserted begins after December 31, 1953.
26 C.F.R. §1.547-7