No domestic or foreign mutual insurer shall issue policies without contingent liability unless, at the time of issue, the insurer has at least four million dollars of surplus. In the case of an alien insurer, policies without contingent liability shall not be issued unless, at the time of issue, the insurer has at least four million dollars of trusteed surplus. However, any mutual insurer that on June 30, 1991, was authorized to issue and was engaged in issuing policies without contingent liability may continue to do so, until July 1, 1994, by maintaining at all times the minimum surplus if a domestic or foreign insurer, and the minimum trusteed surplus if an alien insurer, required at the time of authorization.