"The Goods and Services Tax (GST) is the best indirect tax regime globally and there is no doubt about it and that is why it is adopted in most of the countries. But the way it (GST) was implemented in India is a textbook example of how the tax reform should not be implemented anywhere," he said.
"It should be a case study at Harvard and other universities," said the former finance minister, delivering a lecture on demonetisation and GST at an event in Pune.
Mr Sinha said the recent changes by the government in the GST slabs are "ad-hoc" measures which are not "enough".
He reiterated his demand to rope in economist Vijay Kelkar, the original architect of the GST in India, and make positive reforms to steer the economy out of trouble and added that multiple tax slabs have resulted in "lobbying" for lower rates.
"Factors like non-performing assets of banks and stalled projects are still making adverse impact on the economy," he said.
In an apparent attack on the BJP government at the centre, Mr Sinha said, "If (Robert) Mugabe has to go, nobody is secure. The roots of democracy in India are so deep that no one can move them and if someone attempts to do so, he will be destroyed."
(with inputs from PTI)