Whenever it appears to the Department of Insurance from any proper showing or from any examination made that the capital stock of any domestic stock insurance company is impaired or that its assets are insufficient to justify its continuance in business, the department, in lieu of proceeding immediately in the manner authorized by the Nebraska Insurers Supervision, Rehabilitation, and Liquidation Act, may at once determine the amount of such impairment or deficiency and thereupon issue a written notice to the company requiring its shareholders to make good the amount of the impairment or deficiency with cash or authorized investments or to reduce its capital stock, not below statutory requirements, within a reasonable time not to exceed ninety days from the service of the notice.