Sanjay Nirupam, who quit the Shiv Sena recently following differences with the party leadership, resigned from the Rajya Sabha on Wednesday.
There were differences between him and the Sena leadership over the alleged allotment of Reliance Infocomm shares to a person close to Bharatiya Janata Party leader Pramod Mahajan.
He said the Shiv Sena leadership, buckling under pressure from Mahajan, had asked him not to raise the issue in Parliament.
Nirupam had on Tuesday raised in the Rajya Sabha the issue of the company allotting one crore Reliance Infocomm shares to three unlisted firms at the rate of one rupee each.
Finance Minister P Chidambaram told the House that the government was looking into whether any law had been violated.
