Moving ahead with its plans for a July 1 rollout of the landmark tax reform - a national Goods and Services Tax or GST - Finance Minister Arun Jaitley today said that the four main rates or slabs of the new tax are necessary. "If we don't have that, it'll become a regressive tax. Some goods are essential for the poor," the Finance Minister told parliament. To illustrate the need for different slabs, he said, "A BMW and Hawai chappal (flip-flops) can't have the same tax. What is the goods, who uses it, matters."