For any amended return filed after April 15, 2004, and before the taxpayer is contacted by the Internal Revenue Service or the Franchise Tax Board regarding a potentially abusive tax shelter, then, for taxable years beginning after December 31, 1998, with respect to any understatement of tax related to using reportable transactions as defined in Section 18407, as added by the act adding this section, the taxpayer is subject to interest as provided under Section 19101 but at a rate of 150 percent of the adjusted annual rate established under Section
19521.