"Modi has been misusing his power as the Prime Minister to campaign and propagate for his party BJP," Lalu told the media in reference to Modi's road show in Odisha during the BJP's national executive meeting.
Lalu said it was wrong to misuse facilities provided through public exchequer.
"Modi is free to campaign for his party but not by misusing official position," Lalu added.
He reiterated that the BJP led by Modi would be countered by a united opposition.
"It is a need of the hour to unite to counter the BJP. If we will be united BJP will be nowhere," he said.
The two-day BJP national executive meeting began in Bhubaneswar on Saturday with the lighting of the ceremonial lamp by Prime Minister Modi and party president Amit Shah.
Modi, who landed at the state capital on Saturday afternoon, also held a roadshow from the airport to the Raj Bhavan, covering a distance of around 8 km.