Deputy Chief Minister Ajit Pawar had said last week that more than 10 ministers and at least 20 MLAs have tested positive for coronavirus so far.
The election for the post of the speaker is likely to be held during the ongoing winter session, which ends on December 28. The session had begun on December 22.
The police official said the letter warns that the minister, a resident of Thane city, and his family members will have to pay a "heavy price" for the state government's actions against Naxals.
The BMC wants to promote Marathi at the workplace. The urban development ministry of Eknath Shinde approved this decision recently to woo the Marathi voters ahead of the BMC elections.
Shinde said that contrary to the 'baseless' claims made by the Union Minister, he was very much happy in the Sena, headed by Chief Minister Uddhav Thackeray.
He also claimed that many leaders and ministers in Maharashtra are set to join the BJP.
The accused had posted the alleged defamatory matter on the Facebook page of the minister, he said.