An appeal to the commission must be filed in writing during the period prescribed by statute.
Wis. Admin. Code Tax Appeals Commission TA 1.11
Section TA 1.11 interprets ss. 70.38(4), 70.64(3), 70.995(8), 71.09(13) (d), 71.88(1) (a), 73.01(5) (a), 76.39(4) (c), 76.48(6), and 77.59(6) (b), Stats.