Hazare said he would launch the agitation by the end of the year or early next year.
"During the agitation no party or its member would be allowed to sit on stage. If someone wants to join, he can join the people," he said.
He said that his volunteers will reach Ralegan Siddhi in Maharashtra to discuss on the course of the movement.
In his letter to Modi, Hazare said that while earlier it was mandatory for those covered under the Lokpal to disclose their assets as well as the assets of their family members, the amendment passed in July last year exempted the family members from doing so.
He also accused the Prime Minister of postponing the enforcement of the anti-corruption law by making "one or the other excuse".
"It appears you have no intention to bring Lokpal and Lokayukta Act... And that you don't want to build a corruption-free India," Hazare wrote.
"Looking at the present situation, it appears that no efforts are being made to end corruption and establish effective democracy in the country. Instead, efforts are being made to weaken democracy and strengthen the party.
"Distressed by this, I will pray for the country on the occasion of Mahatma Gandhi's birth anniversary and will launch a 'satyagraha' from his footsteps," he added.
The social activist said that Modi and the Bharatiya Janata Party (BJP) promised many things to the common man including an end to farmer suicides, fair price for agricultural produce, safety of women and solution to all problems of all sections of the society.
Modi also promised getting back the black money stashed abroad within 30 days of coming to power, Hazare wrote.
"But neither the Lokpal and Lokayuktas were appointed, nor the citizen charter enforced. Neither the black money came back from abroad, nor the black money from within the country got exposed through demonetisation.
"Farmer suicides did not stop but have been increasing. They do not get fair price for their produce. There has been no action on the Swaminathan report.
"Women haven't got the security, respect and justice that they deserve. And when it comes to corruption, it has been increasing by the day," Hazare added.
Hazare's remarks has come at a time when BJP-led NDA government has been claiming that it did not allow any scam to take place during the past three years in power. The Modi government has also been claiming it has taken many steps to curb the menace of corruption.