In case a public service commissioner shall fail to attend at any meeting or session of the public service commission appointed for the transaction of business, he shall be subject to a pro rata deduction from his salary; and the executive secretary of said commission or, in his absence, the commissioner or commissioners present shall certify to the auditor of public accounts the number of days such commissioner was absent at each meeting or session. The auditor shall deduct twice the number of days so certified from the time for which the salary of such commissioner may be estimated, unless such commissioner shall make and file an affidavit in the auditor's office that his absence was occasioned by sickness of himself or a member of his family, or by the prevalence of an epidemic or a contagious disease, or by means not within his control.