The Secretary of the Department of Finance is hereby mandated to prescribe, on or before January 31 of each taxable year, a minimum occupancy rate and a daily room rate for motels and inns which will serve as basis for the computation of gross receipts of proprietors, operators and keepers of such establishments. The minimum occupancy and daily room rates shall be prescribed on a regional basis: Provided, That the minimum occupancy rate shall in no case be lower than eighty percent (80%) of motel or inn capacity for establishments situated within Metro Manila, and sixty percent (60%) for establishments situated in other highly urbanized cities and chartered cities: Provided, further, That the imposition of the minimum rates as herein mandaated may be suspended due to force majeure, prolonged labor dispute or other legitimate business reverses.