Adhoc demand of GST on indirect expenses in GST scrutiny - Goods and Services Tax - GST

In GST assessment for FY 17-18, the AO has raised a demand of 18% on a portion of indirect expenses but no reference to the act/rule under which the demand is raised is mentioned. Is this allowed? if this order to be appealed, then what grounds of appeal are available to the assessee? The extract from the order is : The tax payer has furnished the abstract details of other expenses for Rs ______. The details are verified and accepted except the following expenses which are disallowed. Repairs to building Rs 435482 Tax payable @ 18% - Rs 78386 Repairs to machinery Rs 351719 Tax payable @ 18% - Rs 63309 Any suggestions or guidance is welcomed.