"For the last one month, I have been feeling uneasy over the nuclear deal. I am of the opinion that it is not in national interest. I have been opposing it for the last three years," he told reporters with UP Chief Minister Mayawati by his side after a meeting with her.
Siddiqui, also a journalist, said that he was taking this position heeding to the call of his conscience and would oppose the deal to the hilt.
"I am the one who had held Bush's hand and told him that India will not accept the deal," he said.
Though Siddiqui's resignation does not affect Samajwadi Party's numbers in the Lok Sabha, it comes as a huge embarrassment to the party that is in the forefront in attempts to muster numbers for the UPA government in the trust vote on Tuesday.
Siddiqui, who was with the Congress before joining the SP, said he would work with Mayawati for the cause of Dalit-Muslim unity and for the welfare of people of all castes.
Mayawati said that the SP had tried to convince Siddiqui not to leave "but he has come to us leaving behind everything without any expectation". She alleged that SP was supporting the deal because the CBI is tightening its noose around Mulayam Singh Yadav and his family members.