Sonia Gandhi,the driving force and the real President of the Congress Party voted illegally when she was not a citizen of India .
Her name in the voter list document in the image here below.
Illegal registration as a voter:In January 1980, Indira Gandhi returned as Prime Minister. The first thing Sonia did was to enroll herself as a voter. This was a gross violation of the law, enough to cause cancellation of her visa [since she was admittedly an Italian citizen then]. There was some hullabaloo in the press about it, so the Delhi Chief Electoral Officer got her name deleted in 1982. But in January 1983, she again enrolled herself as a voter! Such is her revealed disdain for Indian laws and that is her mindset even today.
Source and citation.