According to Kamran Hussain, a supervisor at the fire station, some weeks ago they had received a telephone call followed by a hand-written note to pay Rs 200,000 as extortion money.
"We informed our superiors in the fire brigade head office, but no action was taken nor any security provided to us," he said.
After a while the extortionists demanded that if the fire brigade station couldn't pay cash they should provide ration for 40 persons, he said.
A senior fire brigade official said the employees have now taken their complaint to the union office of the fire brigade.
Extortion is common in Karachi, Pakistan's biggest city and financial hub, and has resulted in several killings, with traders and businessmen being the main targets.