A group of MPs from Tamil Nadu have threatened to quit unless the government intervenes to halt "atrocities" against fellow Tamils in Sri Lanka.
The 38 deputies from Tamil Nadu are allies of India's ruling Congress party and their resignations could threaten the stability of the national government.
"If the government of India does not come forward to halt the war in Sri Lanka within two weeks, then the MPs from Tamil Nadu would be constrained to give up their posts," the deputies said in a statement.
It urged the government to take "immediate steps to stop the war ravaging the island nation for three decades and claiming several thousand lives including innocent children".
Sri Lanka's ethnic Sinhalese-dominated government is engaged in one of its biggest offensives against the Tamil Tigers, who control part of the north of the island and want to carve out a separate state.
The Sri Lankan government says it has killed around 7,500 Tamil Tigers since January, when it pulled out of a Norwegian-backed truce. The United Nations says 230,000 people have been displaced in the recent wave of fighting.
But the chief minister of the state, M. Karunanidhi, said Indian Tamils could not be "silent spectators of the present atrocities in Sri Lanka".
India intervened in the Sri Lankan conflict in 1987 when it sent its troops to supervise a bilateral peace pact and they ended up fighting the Liberation Tigers of Tamil Eelam (LTTE).
New Delhi withdrew its troops three years later after losing 1,200 soldiers. Since then, India has maintained a hands-off policy towards Sri Lanka.
Bowing to pressure from politicians in Tamil Nadu, India last week expressed "grave concern and unhappiness" at the mounting casualties among Tamil civilians and asked Colombo to "act with greater restraint."
The LTTE was trained and armed by New Delhi in the early 1980s but are now banned. The group was blamed for the 1991 murder of former Indian premier Rajiv Gandhi.