Both the leaders were expelled for indulging in anti-party activities.
BSP General Secretary Satish Chandra Mishra said Nasimuddin has also been accused of accepting money from people in return for work.
Siddiqui, who hails from Banda, was earlier removed as the party in-charge of Uttar Pradesh and appointed as the MP unit in-charge.
Carrying out major organisational rejig, BSP president Mayawati had last month announced the appointment of her brother Anand Kumar as the party vice-president
To revamp her party, Mayawati had also dissolved the existing team of zonal, divisional and district coordinators besides the 'bhaichara' (brotherhood) committees set up to woo different castes and communities like Brahmins, Thakur and Muslims.
BSP had suffered a humiliating defeat in the Uttar Pradesh Assembly elections where the party had managed to secure only 19 seats out of the total 403 seats. In 2014 General Elections, the party had failed to win a single seat.
It had 80 MLAs in the outgoing UP Assembly.
Mayawati had alleged misuse of EVMs in the UP Assembly elections blaming it for her party's poor performance. After the results, Mayawati moved to court against the alleged tampering of EVMs.
(With inputs from PTI)