81. The employer contribution shall be paid in as many equal monthly payments as there are months in the fiscal year of the plan, and not later than the last day of the month that follows each of these months. The monthly payments may, however, represent an hourly rate, a proportion of the remuneration or a percentage of the total payroll for the active members; the rate, proportion or percentage shall be uniform unless it is established by reference to a variable authorized by Retraite Québec.