"The BJP-led (central) government does not want to bring back black money from abroad," Lalu Prasad wrote in his Twitter handle.
"Black money in foreign banks mostly (belong to) Modi's corporate friends and BJP leaders. It is the main reason why the central government is not keen to bring it back."
He said people in villages and towns were feeling cheated by Modi on the issue as the prime minister, while campaigning for the 2014 Lok Sabha polls, had promised to bring back black money stashed abroad.
"Modi promised to deposit Rs.15 lakh in the bank account of everyone but not a single penny was deposited. The government has failed to bring black money nearly one and a half years after coming to power," the former Bihar chief minister later told the media here.
Lalu Prasad's attack on Modi comes days ahead of the first phase of the Bihar assembly elections.
Polling to the 243-member Bihar assembly will take place in five phases between October 12 and November 5. Vote count is slated for November 8.