Accusing Gadkari of taking over land taken away from a farmer in Maharashtra's Vidarbha region, IAC chief Arvind Kejriwal said Gadkari was promoting his business interests at the cost of farmers.
"Whose interests does Gadkari represent? He has a very big business empire. His interests are clashing with those of Vidarbha's farmers?" the activist-cum-politician said.
Gadkari called the IAC's claims "baseless", saying there was no scam. "My conscience is clean. I am ready for a probe."
Banking on a string of official documents translated from Marathi into English, Kejriwal said under rules excess land taken from farmers must be returned or leased to them.
But in this case, he said, the land was handed over to Gakdari's companies by Nationalist Congress Party's Ajit Pawar, who was the Maharashtra irrigation minister until recently.
"This was in violation of rules," he told a crowded news conference. "When farmers protested, they were threatened by Gadkari's henchmen."
Kejriwal added that almost the entire water from government-sponsored irrigation dams were diverted in Maharashtra to power and sugar industries in which Gadkari and other politicians had business interests.
All this was done in collusion with Ajit Pawar, who has been accused of largescale corruption in what has come to be known as the irrigation scam, he said.
While Gadkari wrote letters to the Maharashtra government seeking early payment of money owed to contractors, he never raised issues concerning farmers, Kejriwal said.
"Is Gadkari a businessman or a politician?" he asked, and went on to answer that anyone with business interests could never honestly represent people's interests.
Both the NCP and BJP denied the charges. The BJP called it "a political stunt" while the NCP said the matter was an old one and was already under investigation.
"The entire party, the entire cadre is behind our president Gadkari," veteran BJP leader Sushma Swaraj told reporters.
In response to Kejriwal's remark that it was unfortunate that Gadkari's presidential term had been extended, she added that the BJP was within its right to have anyone as its spearhead.
This was Kejriwal's third major press meet this month. On Oct 5, he alleged collusion between UPA chairperson Sonia Gandhi's son-in-law Robert Vadra, realty major DLF and the Haryana government.
And on Sunday, he accused Law Minister Salman Khurshid and his wife Lousie of corruption vis-a-vis a NGO they run in his constituency Farukkhabad.
Much of what was given out on Gadkari and Ajit Pawar Wednesday came from IAC member Anajali Damania, who said she first learnt of corruption in the building of irrigation dams in Maharashtra through RTI applications.
She said she urged Gadkari, who is from Maharashtra, to take up the issue. But he refused to, reportedly saying: "How could you expect us to speak against (NCP chief) Sharad Pawar?
"Chaar kaam wo hamare karte hain, chaar kaam hum unke karte hain." (They do four favours for us and we do four favours for them.)
Kejriwal said there was a lot of corruption in building irrigation dams. He pointed out that often no canal was built, and so farmers never got the water meant for them.
"There is a proposal to build 71 power plants in Maharahstra. If these are built, not one drop of water will go to farmers because all the water will be diverted for power plants."
The IAC leader alleged that all political parties were in collusion with one another, including the NCP, BJP, Congress and Shiv Sena.
"Gadkari is not a politician, he is not a political leader, he is using the BJP to advance his business interests."
He added: "There will be no probe against Vadra or Khurshid or Gadkari... They are all in league with one another. They are looting the country together."
Asked if the IAC had any expectation from the government, Kejriwal said: "We are not demanding anything from the government. We are demanding from the people of this country... please arise, stand up."