Senior Communist Party of India-Marxist (CPI-M) leader Sitaram Yechury Wednesday said he did not sign the letter, and called it a "cut and paste" job. Mohammad Adeeb, the Rajya Sabha member who had faxed the letter, however, maintained it was genuine.
DMK's member from the Rajya Sabha K.P. Ramalingam, CPI MP Achutan, Nationalist Congress Party MPs Vandana Chavan and Sanjeev Naik, and Congress MPs Marotrao Kowase, Anil Lad and Jayantrao Avale have all denied signing the letter.
"I deny having signed any such letter," Yechury said Wednesday morning.
"The one circulating in cyberspace, now many months after it was allegedly signed, is typed on the letterhead of an MP that carries the insignia of our national symbol, the Ashok Chakra. The heading under which some signatures are appended says: 'Names and signatures of Indian MPs'," Yechury pointed out.
"Strange, which other country's MPs would sign on the letterhead of the Indian parliament? This itself suggests some efforts at cut and paste," Yechury said.
"It is not in my nature to write to presidents of other countries telling them what they should do with the visas of Indian nationals," the CPI-M leader said.
The letter, carrying the signatures of many Indian parliamentarians, was dispatched to both the US president and the British prime minister last year.
A copy of the letter was resent to the White House Tuesday after Bharatiya Janata Party president Rajnath Singh, on a recent visit to the US, asked the government there to issue a visa to Modi.
The letter was forwarded by Rajya Sabha's Independent member Mohammed Adeeb, who expressed shock at Yechury's reaction.
"I am shocked. I don't believe that a person like Yechury is saying something like this. I have his signature. His name is ninth in the list. How can I paste it? I am a member of parliament and I cannot do such a thing. If he says that I have cheated him, I will take him to court," Adeeb said.
"I would welcome it if a probe is done. Will resign from the Rajya Sabha and go to jail if signatures on the letter to Obama are forged," Adeeb tweeted Wednesday afternoon.
Earlier, Adeeb said that "40 MPs from the Rajya Sabha and 25 from the Lok Sabha" signed the letter, which was written in November 2012, before the Gujarat assembly elections.
Congress leader Digvijaya Singh, meanwhile, said: "We have nothing to do with it. It is up to the US government to issue visa to Modi."
Adeeb said that he had on Sunday re-sent a letter written last year by many MPs to the US President.
The letter sought to know if the US government, which in 2002 denied visa to Modi after the communal riots in the state, had changed its policy on the issue.
The earlier letter was sent in 2012, said Adeeb, who added that BJP chief Rajnath Singh's lobbying in the US for a visa to Modi has triggered the issue.
BJP MP from Jharkhand's Lohardaga Sudarshan Bhagat, meanwhile, wrote to Lok Sabha Speaker Meira Kumar urging her for a probe into the alleged forgery. The party also accused the Congress' "dirty tricks department" of being behind the letter.
"These are serious charges and amount to forgery. I have demanded that the speaker order an impartial inquiry, and action should be taken against those responsible," he said.
"The denial by some MPs of having written to Obama shows that this is a clear conspiracy of the dirty tricks department of the Congress. Some MPs have said their signatures were forged. There should be a thorough probe into the matter and the guilty should be booked," BJP spokesperson Prakash Javadekar said.
Modi was denied the US visa for his alleged role in the 2002 Gujarat riots.
The Congress on Wednesday distanced itself from the controversy, saying nothing was discussed in the party.
"The issue has not been discussed in any forum of the party, nor of parliament," Congress spokesperson Raj Babbar told reporters who asked him about the MPs' letter to Obama and the British prime minister.
"The nation is bigger than politics," he said.