Normally a meeting of party MPs is held just ahead of Parliament session but in this case, the winter session is almost three weeks away, so there was speculation over the reason for calling the meeting.
The meeting, which has got underway, assumes significance owing to reports about 86-year-old Thackeray's condition.
Thackeray, who founded the Shiv Sena in 1966, has not been keeping well and, at a Dussehra rally here last week, he addressed party workers via a recorded video message, asking them to support his son Uddhav and grandson Aditya.
"I have collapsed physically...I can't walk...I am tired," he had said in what was seen by many as an indication of his retirement from public life.
Yesterday, Thackeray's nephew, Raj, who formed MNS in 2006, met the ailing Sena chief, his fourth meeting in as many months.