In an effort to reduce their total costs, many companies are now replacing paychecks with payroll cards, which are stored-value cards onto which the companies can download employees' wages and salaries electronically. If the only factor of production that a company varies in the short run is the number of hours worked by people already on its payroll, would shifting from paychecks to payroll cards reduce the firm's total fixed costs or its total variable costs? Explain your answer.