(a) In addition to the penalty imposed by Section 19706 (relating to willful failure to file return, supply information, or pay tax), if any partnership required to file a return under Section 18633 or 18633.5 for any taxable year does either of the following:

(1) Fails to file the return at the time prescribed therefor (determined with regard to any extension of time for filing).

(2) Files a return which fails to show the information required under Section 18633 or 18633.5, that partnership shall be liable for a penalty determined under subdivision (b) for each month (or fraction thereof) during which that failure continues (but not to exceed 12 months), unless it is shown that the failure is due to reasonable cause.

(b) For purposes of subdivision (a), the amount determined under this subdivision for any month is the product of the following:

(1) Eighteen dollars ($18), multiplied by

(2) The number of persons who were partners in the partnership during any part of the taxable year.