Thakur, who has been assisting his wife and RTI activist Nutan Thakur in raising social issues, released an audio tape purportedly containing the voice of the SP chief.
Thakur is an IG-rank officer.
Reacting to the allegation, senior SP leader C P Rai said, "I have not heard the audio but such an allegation appears to be doctored. He (Mulayam) is such a senior leader. I know him for past 30 years... He can never threaten anyone.