In one of the FAQ’s recently released by GST@GOI, it was mentioned that interstate supply of service is taxable and mandatory registration has to be taken. Initially, the law provided that mandatory registration has to be taken in case interstate supply of services is being made, irrespective of the turnover but in 22nd GST Council meeting it was decided to exempt the interstate supply of services upto the turnover of Rs 20 Lakhs.
Link to the FAQ published https://twitter.com/askGST_GoI/status/944191645804670977