(b) There is hereby established a special fund in the State Treasury, separate and apart from all other public moneys or funds of this Commonwealth, to be known as the Workmen's Compensation Supersedeas Fund. The purpose of this fund shall be to provide moneys for payments pursuant to subsection (a), to include reimbursement to the Commonwealth for any such payments made from general revenues. The department shall be charged with the maintenance and conservation of this fund. The fund shall be maintained by annual assessments on insurers and self-insurers under this act, including the State Workmen's Insurance Fund. The department shall make assessments and collect moneys pursuant to this section of the act. Assessments shall be based on the ratio that such insurer's or self-insurer's payments of compensation bear to the total compensation paid in the year preceding the year of assessment. The total amount to be assessed shall be one hundred percent of the amount reimbursed to insurers and self-insurers in the preceding year pursuant to this section, except that the first annual assessment made under this act shall be in the amount of two hundred fifty thousand dollars ($250,000). The department shall give notice to every insurer and self-insurer under this act, including the State Workmen's Insurance Fund, of the amount assessed against such insurer, self-insurer or the State Workmen's Insurance Fund on or before June 30 of the year following the year upon which the assessment is based: Provided, That notice of the first annual assessment under this act shall be given to every insurer and self-insurer under this act, including the State Workmen's Insurance Fund, within ninety days of the effective date of this amending act. Payment of assessments shall be made to the department within thirty days of receipt of notice of the amount assessed, unless the department specifies on the notices sent to all insurers and self-insurers an installment plan of payment, in which case each such insurer shall pay each installment on or before the date specified therefore by the department within fifteen days after the receipt of such notice, the insurer or self-insurer against which such assessment has been made may file with the department objections setting out in detail the grounds upon which the objector regards such assessment to be excessive, erroneous, unlawful, or invalid. The department, after notice to the objector, shall hold a hearing upon such objections. After such hearing, the department shall record its findings on the objections and shall transmit to the objector, by registered or certified mail, notice of the amount, if any, charged against it in accordance with such findings, which amount or any installment thereof then due, shall be paid by the objector within ten days after receipt of notice of the findings. No suit or proceeding shall be maintained in any court for the purpose of restraining or in anywise delaying the collection or payment of any assessment made under this subsection but every insurer or self-insurer against which an assessment is made shall pay the same as provided in subsection (b) of this section. Any insurer or self-insurer making any such payment may, at any time within two years from the date of payment, sue the Commonwealth in an action at law to recover the amount paid, or any part thereof, upon the ground that the assessment was excessive, erroneous, unlawful, invalid, in whole or in part, provided objections, as hereinbefore provided, were filed with the department, and payment of the assessment was made under protest either as to all or part thereof. In any action for recovery of any payments made under this section, the claimant shall be entitled to raise every relevant issue of law, but the findings of fact made by the department, pursuant to this section, shall be prima facie evidence of the facts therein stated. If it is finally determined in any such action that all or any part of the assessment for which payment was made under protest was excessive, erroneous, unlawful, or invalid, the department shall make a refund to the claimant out of the appropriation specified in subsection (c) as directed by the court.