A comprehensive multistage Value Added Tax (VAT) system, viz., Goods and Services Tax (GST), is introduced in India since 1 July 2017. GST encompasses various taxes from Union and State indirect tax bases and it is a dual VAT system with concurrent taxation power to Union and State governments. It was envisaged that removal cascading of taxes and enshrining destination based consumption tax system under GST will encourage investment and improve ease-of-doing business in India. Though it is not right time to comment on success or failure of Indian GST system unless the tax system stabilizes, so far revenue mobilization from GST is not encouraging. The shortfall in GST collection has been acknowledged in the ‘Medium Term Fiscal Policy cum Fiscal Policy Strategy Statement’ of the Union Budget 2019-20. The genesis of revenue shortfall may be design and structural in nature and/or compliance and tax administration related. However, the uncertainty surrounding GST revenue collection is an issue which needs an in-depth assessment for fiscal management of Union and State governments. The impact of revenue uncertainty will not be restricted to Union finances alone; it will spill over to state finances through inter-governmental fiscal transfers. Therefore, depending on seriousness of the uncertainties associated with GST revenue collection, devising an inter-governmental fiscal transfer framework may be a challenging task for the Fifteenth Finance Commission. Given the information available in the public domain, this paper attempts to explore possible causes of revenue shortfall and assess possible impacts of revenue shortfall on Union and State finances.