40 Pa. Stat. § 784
The board of directors of any employers' mutual liability insurance association shall determine the amount of the premiums which the subscribers of the association shall pay for their insurance, in accordance with the nature of the business in which such subscribers are engaged, and the probable risk of injury to the employes under existing conditions. They shall fix premiums at such amounts as, in their judgment (subject to the approval of the Insurance Commissioner), shall be sufficient to enable the association to create and maintain the surplus provided in section six hundred and forty-three (643) of this act, and to pay to its subscribers all sums which may become due and payable to their employes under the provisions of article three of "The Workmen's Compensation Act of one thousand nine hundred and fifteen," or any amendment or revision thereof, and also the expenses of conducting the business of the association.
In fixing the premium payable by any subscriber, the board of directors may take into account the condition of all the property or premises of such subscriber, in respect to the safety of those employed therein or thereon, as shown by the report of any inspector appointed by such board.
The board of directors may, from time to time, change the amount of premiums payable by any of the subscribers as circumstances may require, and the condition of the property or premises of such subscriber in respect to the safety of their employes may justify. They may increase the premiums of any subscriber neglecting to provide safety devices required by law, or disobeying the rules or regulations made by the board of directors in accordance with the provisions of section six hundred and thirty-eight (638) of this act.
No policy of insurance issued to any subscriber shall be effective until he shall have paid the premium so fixed and determined.
40 P.S. § 784