In Keystone Coal Mining Corporation v. Workmen's Compensation Appeal Board (Wolfe), 673 A.2d 418 (Pa. Cmwlth. 1996), the Court held that a 1993 amendment to section 204(a) of the Act, 77 P.S. 71(a), which expanded employers' right to credit for unemployment compensation benefits received by a claimant, could not be applied retroactively to a claimant receiving both workers' compensation and unemployment benefits prior to the amendment's effective date because the amendment affected the claimant's substantive right, as fixed by the prior version of the statute, to collect both benefits simultaneously.