He claimed that Shiv Sena knew that the BJP was already planning to nominate someone from Chintaman Wanga's family for the by-election, scheduled on May 28.
Lauding Mr Wanga's association with the BJP, Chief Minister Fadnavis said the leader had represented the party's ideology.
In a jolt to its ally BJP, Shiv Sena fielded Shriniwas Wanga for the by-election after his father and sitting BJP MP from the Palghar seat, Chintaman Wanga, died.
Mr Fadnavis, at an earlier rally in the district, said he had told Shiv Sena chief Uddhav Thackeray that the BJP was planning to give a ticket to a member of Chintaman Wanga's family for the by-election.
"Our ally (on one hand) was welcoming our decision to give ticket to the Wanga family and on the other hand hatching a conspiracy," the chief minister said at a campaign rally in Palghar's Nallasopara area last night.
Chintaman Wanga's wife had yesterday filed a complaint of model code violation against the BJP, accusing the party of using her husband's pictures on publicity material for the upcoming by-election illegally.
However, Mr Fadnavis said only the BJP had the right to use the late leader's photos. "Only we have the right to put up Chintaman Wanga's photo. He wasn't an individual but our ideology," he said.
Urging the people of Palghar to vote fearlessly without succumbing to any threats, the chief minister said those come between the BJP and the people will be "crushed".
For the by-election, the BJP has fielded Rajendra Gavit, who recently left the Congress to join the BJP.
Mr Fadnavis asserted that Mr Gavit was the right successor to Chintaman Wanga.
"Why vote for those who don't know whether they exist or not. Rajendra Gavit is like (Chintaman) Wanga who struggles for people...send him to the Modi team (Parliament)," he said.
Delhi BJP chief Manoj Tiwari also spoke at the rally.
Apart from the BJP and Shiv Sena, the Congress is also contesting the by-election to the tribal-dominated constituency, located about 110 km from Mumbai, and has fielded former MP Damodar Shingda.
Local outfit Bahujan Vikas Aghadi (BVA), which has three MLAs in total six Assembly segments in the Palghar constituency, has nominated former MP Baliram Jadhav.