The communist parties that have provided the Indian government with a parliamentary majority for four years are to withdraw their support from the governing coalition in protest over a civilian nuclear pact with the United States.
The communist parties had said they would withdraw if the government formally went ahead with the deal with the International Atomic Energy Agency. Prime Minister Manmohan Singh said yesterday that move would come "very soon."
It was the final straw for the left.
"That time has come," Prakash Karat, head of the Communist Party of India (Marxist), India's biggest communist party, told reporters.
Karat said the communist parties would formally announce their withdrawal in a meeting with India's president tomorrow.
The withdrawal will likely lead to a vote of confidence in the government. The government has lined up support from a regional party to provide it with a parliamentary majority and hopes to avoid early elections if the communists pull out.
Prime Minister Singh arrived in Japan on Monday for a G8 summit where he is expected to tell US President George W. Bush - the man who shook hands with Singh on the accord at the White House in 2005 - that the delayed deal will go ahead.
The pact would be a major success for Singh, giving India access to US nuclear fuel and technology and moving the Asian giant's trade and diplomatic relations closer to the West.
The withdrawal could plunging India into more political uncertainty that has already hit markets. The government believes it will survive the vote, having won the backing of the regional Samajwadi Party.