The Muttahida Qaumi Movement (MQM) and traders of Karachi Saturday observed “Black Day” across Sindh against money extortion ‘mafia’, with business activities and educational institutions closed in Karachi.In few incidents of violence, miscreant set on fire three busses in different areas of Karachi during strike.The traders had announced to observe complete shutter down strike against the extortion while educational institutions, business centers, petrol pumps and hotels remain closed. Public transport is suspended in the city while a large number of local passengers had faced problems in traveling.The issue came in light after a large number of small to large business units received calls from criminal groups working in the city to send them “extortion money”.This led to widespread protest from the trade and business community of the city.The MQM and other political parties and social organizations have supported the traders strike.All examinations of Intermediate Board have been postponed and new date for the exams will be announced later. Federal Urdu University and Dao University have also cancelled examination papers that were scheduled to be held on Saturday.On Monday, the MQM lodged a strong protest in National Assembly against the rising incidents of extortion in Karachi.The party also threatened to disrupt President Asif Ali’s address to joint sitting of the Parliament on Saturday if government did not act against the extortionist mafia operating in the metropolis.However after President’s assurance MQM decided not boycott Zardari speech to the Parliament.MQM’s Wasim Akhtar said the Government of Sindh has badly failed to act against extortionists. “Provinces would not get their share of NFC Award if incidents of extortion did not come to an end in Karachi,” he warned.“We want complete removal of extortionist mafia,” he said. Akhtar said traders’ community is on roads against the menace.MQM leasder Altaf Hussain appealed the protesters to remain calm and peaceful during the strike.