The Public Utilities Commission, in determining the allowance for materials or services to be included in costs of operations for rate-making purposes, may disallow any unreasonable profit made in the sale of materials to or service supplied for any public utility by any firm or corporation owned or controlled directly or indirectly by such utility or any affiliate, subsidiary, parent company, associate or any corporation whose controlling stockholders are also controlling stockholders of such utility. The burden of proof shall be on the public utility to prove that no unreasonable profit is involved.
SDCL 49-34A-19.2