"My principles did not allow me to compromise with the political compulsion. My conscience did not allow me to vote for Walmart," Singh, who was union rural development minister in the UPA I government, told PTI here.
The RJD national vice president said he had a long argument with Prasad on Tuesday to stress that the party's ideological foundation was based on teachings of socialists like Rammanohar Lohia and Jayprakash Narayan who always worked for welfare of poor and RJD should not support FDI.
While Singh abstained from voting in the House during voting on FDI last evening, three other party MPs including Lalu Prasad voted with the Congress.
Leader of Opposition in the Assembly Abdul Bari Siddiqui, however, said "there is no crack in the party.
"RJD had not issued any whip on the FDI issue hence an individual like Raghuvansh Prasad Singh took a personal decision on the subject ... Moreover the episode reflects democratic traditions within the party," Siddiqui, a senior RJD leader, said.
Senior JD(U) leader and Rural Works Minister Bhim Singh claimed that people like Raghuvansh Prasad Singh who always upheld socialist ideology did not have much respect within RJD and people like him should walk out of the party.
"How come Lalu Prasad who always talks about social justice and poor went out of the way to support FDI which aims to render the poor jobless," the JD(U) minister, who himself recently switched sides to the ruling party from RJD, asked.
"Lalu Prasad is trying to woo Congress president Sonia Gandhi compromising the ideology of the party and in such a circumstance people like Raghuvansh Prasad Singh is bound to feel suffocated," he added.