In addition to the penalty under sub. (4) (a), a taxpayer who files an amended return after May 31, 2008, and before the taxpayer is contacted by the internal revenue service or the department regarding a reportable transaction is subject to a penalty in an amount equal to 50 percent of the interest assessed under s. 71.82 on any reportable transaction understatement, as determined under sub. (4) (b), for the tax period for which the taxpayer files an amended return.

If the internal revenue service or the department contacts a taxpayer after May 31, 2008, regarding a reportable transaction and the taxpayer is contacted before the taxpayer files an amended return with respect to that transaction, the taxpayer is subject to a penalty in an amount equal to the interest assessed under s. 71.82 on any reportable transaction understatement, as determined under sub. (4) (b), for the tax period for which the internal revenue service or the department contacts the taxpayer.