A bill that will allow the United States to sell nuclear technology to India compromises India's independence, its main opposition party said on Sunday, adding that the "humiliating" law should be rejected.
Legislation sailed through Congress early on Saturday, ending the isolation imposed after New Delhi developed nuclear weapons in contravention of international standards.
The deal, first agreed in July 2005, has caught the imagination of many in India and is seen as a major move towards becoming a regional power. But it has also attracted criticism after it was modified in the US legislature.
In a sign of the battle the government faces, the Bharatiya Janata Party, which ruled the country between 1998 and 2004, said early fears the United States was only interested in capping India's nuclear weapons programme "stood confirmed".
A BJP statement said the bill did not deliver full civil nuclear cooperation, imposed "rigorous" assessment obligations, failed to guarantee uninterrupted fuel supplies for civilian reactors and prevented India from reprocessing spent fuel.
It also banned future nuclear tests and rendered the weapons programme "subject to intrusive US scrutiny". Strategic analysts and members of the Indian nuclear establishment have cited similar concerns.
They argued against inspections and said the deal would constrain India's military nuclear programme by separating it from the civilian side.
An earlier draft stated that cooperation would depend on India's support for international efforts to restrain Iran's nuclear programme, rankling New Delhi.
That provision was watered down, but the US president will have to give yearly assessments.
The BJP said: "The US Act seriously compromises the independence of our foreign policy."
"India is not just to toe the line of the US in regard to Iran, it is being afforded this (deal) on the grounds ... that its foreign policy will be 'congruent' with that of the US"
"The Act aims at capping, rolling back and eventually eliminating India's nuclear weapons capability. By going in for agreement under this legislation, the government is binding India's future - in security as well as technical advancement."
Prime Minister Manmohan Singh has promised parliament his government would not accept a significantly amended deal.