Every commercial ferry shall, on or before the date specified by the commission for filing annual reports under RCW 81.04.080, file with the commission a statement on oath showing its gross operating revenue from intrastate operations for the preceding calendar year, or portion thereof, and pay to the commission a fee of two-fifths of one percent of the amount of gross operating revenue: PROVIDED, That the commission may, by rule, set minimum fees that do not exceed the cost of collecting the fees. The commission may by rule waive any or all of the minimum fee established pursuant to this section. The percentage rate of gross operating revenue to be paid in any year may be decreased by the commission by general order entered before March 1st of such year.