The Narendra Modi government has put the Opposition parties in a fix. After becoming part of the wide consensus over the government's push for the Goods and Services Tax (GST), now they are shying away, trying to distance themselves from the mega GST launch function on Friday midnight.The fact that the GST bills could pass in Parliament and the all-party GST Council could frame all the rules indicates there was an all-party consensus on India's biggest tax reform. But if the opposition parties attend the launch function now, it will seem a big achievement of Prime Minister Narendra Modi—a politician who is seen as polarising by the opposition -- is able to create an all-party consensus, which the Congress party could not in nearly a decade of its efforts to push the tax reform.There is a talk of many parties boycotting the launch function, expressing their concerns over a hasty implementation of the GST. There is intense lobbying among opposition parties to boycott the function. The opposition meeting on June 28, when presidential candidate Meira Kumar will file her nomination papers, will decide how many parties will stay away from the function.PM Modi will like to see all the major parties attend this function, which will be an opportunity for him to project himself as a consensus-building statesman who could bring all the opposition parties on one stage for the greater good of the country.Wary of the opposition moves to boycott the launch function, the government has played a clever move: it has sent a personal invitation to former prime minister Manmohan Singh.It was Manmohan Singh who had whole-heartedly supported the GST bills and had told his own party, the Congress, not to break the consensus over a step that is favourable for the country. Manmohan had told his party that it would send a wrong signal for a new federal framework. In fact, the Congress has claimed credit for introducing the mega reform even though it failed to create a consensus over it in nearly a decade.After backing the GST so vocieferously, Manmohan Singh cannot afford to stay away from the launch function. If Manmohan Singh attends, his party too will have to. And if both Manmohan Singh and the Congress attend, it won't matter much if a few regional parties such as Trinamool Congress stay away.By having Manmohan Singh by his side, PM Modi will also blunt any future criticism of the GST by the Congress.