Prime Minister Narendra Modi addressing BJP workers in Bhopal. (Press Trust of India photo)

Prime Minister Narendra Modi made a scathing attack on the Congress this morning, taking on Sonia Gandhi with words that played on her jibe at him earlier this week. He was addressing BJP workers in Bhopal.Lambasting the opposition party for obstructing key reforms like the Goods and Services Tax in Parliament, the Prime Minister said, "They did not let Parliament work... the 'hawalabaaz' are troubled by law passed against black money."The Congress president had accused the Prime Minister of "hawaa baazi (making hollow promises)" while addressing top leaders of her party earlier this week. She expressed concern that "the economy is on a downward slide while prices continue on their unrelenting rise."The Prime Minister, who won the national election last year on the promise of an economic revival, hit back at Mrs Gandhi saying, "To those who have been rejected by the people, I appeal to them for the pride of democracy, to fend economic dangers off and work with us...we had hoped they would help Parliament enforce reforms. But they refuse to do so."On Wednesday, the Modi government dropped a plan to reconvene Parliament to secure approval for the country's biggest tax reform ever, the Goods and Services Tax or GST, which will make India a single market with one tax.Finance Minister Arun Jaitley said it was forced to do so as talks with the Congress had failed to yield results. "The Congress Party is holding back the GST. It has only two options to block the bill, either by disturbance or delay," Mr Jaitley said.The retreat, a new setback to PM Modi's plans to revamp the economy, came a day after the Prime Minster sought to reassure an increasingly sceptical business community that India can withstand global market turbulence and China's slowdown.Mr Jaitley said he would continue efforts to talk to political parties and meet an April 2016 deadline for the implementation of GST, that foreign and domestic companies consider one of the best ways to spur growth.The decision followed a series of setbacks. With the crucial Bihar election looming, PM Modi last month dropped a bill to make it easier for industry to acquire land after the opposition denounced it as anti-farmer.The government needs opposition support to pass bills as it lacks a majority in the upper house.