The chief minister of India's Uttar Pradesh state has accused the Congress party of tapping the phone of a top official of his Samajwadi party.
Mr Yadav said Congress was conspiring to bring him down
Mulayam Singh Yadav said Congress was trying to overthrow his government.
He said he had evidence the private phone of his party's general secretary had been tapped since October.
A federal home ministry official said the accusations were "totally baseless" and that documents put forward as evidence were "clearly forged".
Addressing a press conference in Lucknow, Mr Yadav, also the leader of the regional Samajwadi party, said he had "full evidence" to prove the private phone of general secretary Amar Singh had been tapped.
Mr Yadav called the action "unethical" and said it was "against the norms of democracy".
He said Congress had been "hatching a conspiracy to topple the government by defaming it ever since it come to power and this incident is part of that bigger ploy".
Mr Yadav said he had copies of letters which he said were written by top officials in the Delhi police and the federal home ministry ordering their subordinates to tap the phone.
However, the joint secretary in the federal home ministry, LC Goyal, said no such instructions had been issued.
Mr Goyal said the matter had been thoroughly examined by the Delhi police commissioner and the principal secretary in the ministry.
He said according to the documents and the evidence available it appeared to be "prima facie a clear case of forgery".
He said a case of forgery, cheating and criminal conspiracy had been registered with the Delhi police.
A Congress spokesman in Delhi, Anand Sharma, also said the allegations were "baseless".
He said it had become a "habit" with the Samajwadi party to make "dramatic" allegations against Congress.