"You tell people that you want to create a corruption- free India. But you weaken the Lokpal legislation which will help curb corruption," Hazare said in a letter to Modi.
"There is a difference between what you say and what you do. That is why I asked activists in many states about the agitation. They said that March 23 being Shahid Diwas, we should launch the agitation in Delhi on that date," Hazare wrote.
"Please let us know the difficulty in appointing Lokayukt in states where your party (BJP) is in power," Hazare said.
"Lokpal legislation takes five years but the legislation to weaken it is passed in just three days. This shows that it is not the intention of your government to curb corruption," he said.
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Hazare, who has been the face of the Lokpal movement, had said while addressing a meeting of his supporters at Ralegan Siddhi village in Maharashtra's Ahmednagar district on Tuesday that this agitation will be a satyagrah for Jan Lokpal, farmers' issues and poll reforms.
"At least 12 lakh farmers have committed suicide in the last 22 years. I want to know the number of industrialists committing suicide during this period," he had said.
Hazare has been demanding Jan Lokpal to keep a check on corruption.
He went on a 12-day hunger strike in 2011 after which the then UPA government accepted the demand in principle.
Hazare later launched a fast, which enjoyed a huge popular support across the country. The UPA government subsequently passed the Lokpal bill.