Writing a letter to the Union Home Minister P Chidambaram seeking adequate security, Mr Joshi on Monday, Jul 9 revealed the news in the public.
In his letter, Mr Joshi mentioned about the different numbers from which he has been receiving the calls. He also mentioned a person's name from whom he allegedly had received a threatening note.
The person, who has been accused of sending the note to Mr Joshi, has been identified as Rasool Khan. However, his whereabouts and further details are yet to be tracked by the investigative team.
Joshi, an RSS favourite, has been a vocal critic of Modi since long and has been maintaining that the party was above any individual. Joshi always criticises Modi's style of working as the Gujarat Chief Minister.
Joshi disapproved the BJP deviating from the RSS philosophy and led a campaign to counter senior BJP leader LK Advani's efforts to start a debate over the role of Mohammad Ali Jinnah in India's movement for independence.
In 2007, ending all speculation about the status of Joshi, the RSS said he continued to be a sangh pracharak.
Reacting to reports that he had been stripped of the pracharak status, former RSS spokesperson Ram Madhav said no such decision had been taken. The statement was significant for Joshi who had been brought to the BJP from the RSS and was dropped as the party's general secretary in a reshuffle of BJP office-bearers by the then party President Rajnath Singh.
Joshi had quit in 2005 following his involvement in a controversial CD row. He later joined BJP but once again he was forced to resign from BJP national executive following the adamant demand of Mr Modi.
Joshi always remains in the news over the differences between him and Mr Modi. Recently, he hogged the limelight after posters featuring him were put outside Bharatiya Janata Party's office in Ahmedabad and New Delhi.