Wis. Stat. § 71.35
In addition to the other taxes imposed under this chapter, there is imposed on every tax-option corporation, except a corporation that qualifies for the exception under section 1374 (c) (1) of the internal revenue code and that has not elected to change from tax-option status under s. 71.365 (4) (a) for that taxable year, that has a net recognized built-in gain, as defined in section 1374 (d) (2) of the internal revenue code, during a recognition period, as defined in section 1374 (d) (7) of the internal revenue code as modified by this section, a tax computed under section 1374 of the internal revenue code except that the rate is that under s. 71.27 (2), the net recognized built-in gain is computed using the Wisconsin basis of the assets and the Wisconsin apportionment percentage for the current taxable year, the taxable income is the Wisconsin taxable income and the credit and net operating losses are those under this chapter rather than the federal credits and net operating losses. The tax under this section does not apply if the return is filed pursuant to a federal S corporation election made before January 1, 1987, and the corporation has not elected to change its status under s. 71.365 (4) (a) for any intervening year. If a corporation that elected to change from tax-option status under s. 71.365 (4) (a) subsequently elects to become a tax-option corporation, its recognition period begins with the first day of the first taxable year affected by the subsequent election.
Wis. Stat. § 71.35