The state is scheduled to go to the polls next week in the fifth and final phase of India's staggered month-long elections.
Party officials, however, denied the decision was sparked by security fears linked to the war on Tamil Tiger rebels in nearby Sri Lanka, which has prompted furious protests in India's Tamil Nadu state.
Sonia Gandhi's presence in the area is particularly sensitive because her late husband, former prime minister Rajiv Gandhi, was killed in a Tamil Tiger suicide attack in Tamil Nadu in 1991.
Last month Indian security officials reportedly warned that Sonia and her two children could be targeted by Sri Lanka's Tamil Tigers -- currently facing a massive Sri Lankan military onslaught -- and ordered security be stepped up.
But a Congress Party spokesman said a rally in state capital Chennai and one in the territory of Pondicherry, a Tamil-majority former French colony, were called off because Tamil Nadu's chief minister was in hospital with a fever.
The two had been