When it is determined by the Board that a lay-off is necessary and where natural attrition, transfers, sabbaticals and leaves of absence do not affect the necessary reduction in staff, the Board shall develop a seniority list as hereinafter provided. Such a list shall contain the names of those tenured teachers having the least seniority identified in sufficient numbers to enable the Board to lay-off the required number of teachers after taking into account the special subject, program and administrative needs of the Board. The Association and the teacher shall be permitted a period of ten teaching days after posting of such list to protest in writing to the Board any alleged omission or incorrect listing, but such protest shall be confined to errors in or changes occurring since the posting of the last seniority list.