"Today would be remembered as a black day in the history when a highly respected Dalit leader was not allowed to raise the voice of poor in the Rajya Sabha," Lalu said reacting to Mayawati's resignation.
"We are with her," Prasad said.
Mayawati's current term would have ended in April next year and her party, with just 18 MLAs in the UP Assembly, is not in a position to send her to Rajya Sabha.
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"Chanakya had said that an assembly (of people) where a person is not allowed to speak through the force of brute majority is no assembly," he said.
Lalu Prasad's support to Mayawati is being seen as a part of his efforts to bring her and Samajwadi Party leader Akhilesh Yadav together. He has invited the two leaders to his party's August 27 rally here.