If your Aggregate Turnover for the period July 2017 to March 2018 exceeded Rs. 2 crore, then you are required to file FORM GSTR-9C ( Reconciliation Statement and Audit Report ) for FY 2017-18 and get it certified by a Chartered Accountant or a Cost and Management Accountant by virtue of Section 35(5) of the CGST Act 2017 read with Rule 80(3) of the CGST Rules 2017.
The same has also been clarified by the CBIC Department by way of Press Release.