"It is a matter of lament that the Prime Minister could not spare even five minutes to be present during the passage of the legislation which he had labelled as one of the most progressive and revolutionary," party spokesman Jairam Ramesh told reporters here.
"The Prime Minister was not on a foreign tour. He was sitting in his office in Parliament. It is a contempt of Parliament," he said.
Ramesh said that this was the first occasion in independent India that the Prime Minister was not present while passage of a Constitution amendment bill.
"The PM could tweet about GST, but couldn't be present in Rajya Sabha. Parliament appeared to be PM-mukt", he said, noting that Modi was not present in Lok Sabha when the GST bill was passed last year.
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Ramesh suggested that Prime Minister could have deliberately stayed away from Parliament given the fact that earlier as Gujarat Chief Minister, he had opposed GST for three years.
He made a strong pitch that CGST and IGST bills being brought in the winter session should be treated as financial bills and not as money bills, saying that all opposition parties are favouring such a course.
"Congress wants a GST which will benefit the common man. If the GST rate is about 18 per cent, it will have an impact on inflation," he said.