Among the leaders said to have received the extortion letters are Farooq Sattar, Haider Abbas Rizvi, Khalid Maqbool Siddiqui, Nasreen Jalil, Babar Ghauri and Abdul Rasheed Godil.
"We are getting these threats even on our mobile phones via calls and SMS. We have been told to pay up to rupees five million within one week otherwise we will be targeted along with our families," Sattar, a sitting parliamentarian and member of the MQM central committee, told reporters here.
The MQM leader they were targeted for party's ideological stance against the militants.
"We are being targeted because of our ideological views and because we have been speaking out for years now against the growing influence of the Taliban and other militant outfits in a city like Karachi which is the economic heart of Pakistan," Sattar said.
He said a copy of the letter received on September 15 had been sent to Prime Minister Nawaz Sharif.
The MQM, the single largest party in Karachi and some urban areas of the Sindh province, has been the target of several bomb and gun attacks by Taliban militants in the past, with at least three MQM leaders killed in such attacks.