Shiv Sena, which has been blowing hot and cold over joining the new government, said, "We have constantly been humiliated by the BJP, which has not gone down well with our MLAs.
"As our MLAs feel that BJP did not give us due respect, why should we attend the oath-taking ceremony" Sena MP Vinayak Raut told reporters after meeting party president Uddhav Thackeray.
The tough posturing by Sena came hours after BJP said no minister from that party was likely to be inducted tomorrow.
"It seems unlikely that any Shiv Sena minister will be sworn in tomorrow. Talks with Sena are on in an amicable atmosphere for a possible tie-up in Maharashtra but there has been no outcome yet," BJP general secretary Rajiv Pratap Rudy said.
Maintaining that BJP was looking forward to a decision soon, he said," This may not happen tomorrow."
When asked if talks between Shiv Sena and BJP leaders for discussing a possible alliance had been called off, Raut said no talks had been scheduled, so there was no question of cancellation.
Earlier in the day, Sena MP and spokesman Sanjay Raut had said "positive talks" were on between the two parties and extended best wishes to Fadnavis and his team.
44-year-old Fadnavis, a fourth-term MLA from Nagpur, will be administered the oath of office by Governor C Vidyasagar Rao at Wankhede Stadium in the presence of Prime Minister Narendra Modi, several of his Cabinet colleagues, Chief Ministers of BJP-ruled states, corporate leaders, Bollywood stars and other celebrities.
A small Cabinet of about a dozen ministers including state BJP Core Committee members Eknath Khadse, Sudhir Mungantiwar, Vinod Tawde and Pankaja Munde besides MLAs from Schedule Castes and Scheduled tribes is also likely to be sworn in.
"A slim and trim government will take oath tomorrow," a BJP leader said.
BJP had emerged as the single largest party in the 288-member state Assembly with 122 seats but one of its MLAs Govind Rathod died.
Though technically it will be a minority government until Sena joins it, declared support from 41-member NCP will act as a hedge for the BJP dispensation. It also has the support of several independent MLAs and those from some smaller parties.