"Shiv Sainiks put up boards appealing leaders to show self respect. Hope Shiv Sena leadership takes signals and prepare to sit in opposition," Raut said in a post on Twitter.
In another tweet, Raut said media reports indicate that BJP and Sena are discussing 28:14 formula for alliance government.
"Is this acceptable to Uddhav Thackeray and why?" he asked.
In an earlier tweet, Raut said the BJP is trying to push Shiv Sena to a corner as much as possible.
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When asked to comment on Raut's statements, Sena chief Uddhav Thackeray's public relations officer Harshal Pradhan said, "We don't know if Shiv Sainiks have put up boards. Raut is not a party spokesman and does not hold any post in the party."
Back channel talks were said to be on between BJP and estranged former ally Shiv Sena for forming a coalition government.
BJP, which has emerged as the single largest party in the 288-member Assembly with 122 seats, has already been offered outside support by 41-member NCP.