Communist allies of India's government have given it a deadline to say if it will proceed with the civilian nuclear deal with the US, reports BBC.
The Communists, who say they will withdraw support from the government if it goes ahead with the deal, want the government to inform them by Monday.
The Communists have 59 members in the lower house of the parliament.
They say the deal would give the US undue influence over India's foreign and nuclear policy.
India is under pressure from Washington to sign the deal before the US presidential elections in November.
The government is holding talks with another party to bolster its support.
Reports suggest that the Congress party-led coalition would go ahead with the deal.
India's foreign secretary Shiv Shankar Menon has said that Indian Prime Minister Manmohan Singh will meet US President George W Bush on the sidelines of the G8 summit in Tokyo Wednesday.
Correspondents say Mr Singh is expected to tell Mr Bush that India would be going ahead with the deal despite the opposition from its allies.
The deal now needs to be approved by the UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), as well as by the 45-nation Nuclear Suppliers Group, which regulates global civilian nuclear trade.
Then it has to be presented to the US Congress for final approval.
The Communist allies met on Friday to discuss the "modalities" of withdrawing support to the government.
"We wish to know definitely whether the government is proceeding to seek the approval of the safeguards agreement by the board of governors of the IAEA," said Prakash Karat, head of the Communist Party of India (Marxist), reading out a letter addressed to the government.
"Please let us know the position by July 7, 2008."
Another Communist leader AB Bardhan said there was no confusion about the Communists withdrawing support if the government went ahead with the deal.
"Only modalities like timing and writing to the president will have to be decided," he said.
Analysts say the decision to withdraw support could come in the next few days, plunging India into a fresh round of political uncertainty.
Separately, the Congress party is holding talks with the regional Samajwadi Party Friday to secure its support for the deal to compensate for the loss of its Communist allies.
If the Communists withdraw support, the ruling coalition would be reduced to 226 members in the 543-member parliament, a good 46 seats behind the majority mark of 272.
