Regulations Governing the Employment of Foreigners by Elementary and Secondary Experimental Education Schools and Institutions Article 7

A school or an institution may employ a foreigner to teach subjects or foreign language courses. The maximum number of foreign employees that it may employ shall be calculated by multiplying the total number of classes approved by the competent authority concerned by the number of class periods specified in the experimental education plan or business plan for each class each week for each related subject or foreign language course, and then dividing the resulting product by sixteen class periods. The resulting number is the maximum number of foreigners that may be employed. If the resulting number is less than one, it is counted as one person.If the foreign employees referred to in the preceding paragraph who teach academic subjects or foreign language courses are employed on a part-time basis, every three such persons is counted as being the equivalent of one full-time employee.If two or more schools or institutions jointly employ the foreigners referred to in the preceding paragraph, the total number of classes that they teach and the number of hours that they work each week may be counted in aggregate.
中文原文 高級中等以下實驗教育學校及機構聘僱外國人辦法第7條
學校、機構得聘僱從事學科、外國語文課程教學之外國人,其人數上限之計算依各該主管機關核定總班級數,乘以實驗教育計畫或經營計畫所定每班每週之該學科或外國語文課程節數,除以十六節,等於最高聘僱人數,所得之數額不滿一人,以一人計算。
前項從事學科、外國語文課程教學之外國人為兼任者,每三人以專任一人計算。
二以上學校、機構合聘前項外國人者,其總班級數及每週工作時數,得合併計算。

English translation for reference only; the Chinese text prevails. Not legal advice.