CHANDIGARH, April 19: The Electricity Street Light Employees' & Workers Union has threatened to stage a protest dharna if their demands are not met with by the Municipal Corporation by April 20.Vachaspati, the general secretary of the union, said they had submitted their demand charter to the concerned officials of the corporation but no response from any official has been received.The employees said they would stage the dharna in front of the office of the Electricity Sub Division of Municipal Corporation, Industrial Area, Phase-I tomorrow.