Six ministers from a regional party inside India's ruling coalition resigned on Friday in a split over economic reforms, an official in the prime minister's office said.
"They have submitted their resignations and gone to meet the president," said the official, who spoke on condition of anonymity.
The Trinamool party, based in West Bengal state, has withdrawn support from the coalition dominated by the Congress party over a row about foreign direct investment in India and rises in subsidised energy prices.
Prime Minister Manmohan Singh's government announced a blitz of reform measures last week, including allowing foreign groups to invest in the retail and aviation sectors and hiking diesel prices by 12 per cent.
Trinamool, which has frequently opposed policy changes since elections in 2009, holds the railways portfolio in the cabinet and has five junior ministers in other positions in the government.
The move leaves Singh's Congress party running a minority government, dependent on outside support from other parties and vulnerable to falling before the scheduled date for the next elections in 2014.
There appears no immediate danger of collapse after the regional Samajwadi Party (SP) from northern India, whose 21 MPs generally back the government from outside the coalition, vowed on Friday to keep up its support.