The 2003 letter was written in Mr Cunliffe's capacity as the MP for New Lynn after he was "approached by my constituent Donghua Lui [sic] who is concerned at the time it is taking to process his Investment Category application".
Mr Cunliffe this week denied any involvement with Liu's residency bid after the New Zealand Herald revealed the property developer paid $15,000 at a Labour Party fundraiser for a book signed by Helen Clark in 2007.
Mr Cunliffe yesterday said he did not lie about writing the letter.
"I did not advocate for him. A letter has just come to my attention which is 11 years old. I simply asked how long a processing process would take."
Mr Cunliffe said he had no recollection of meeting Mr Liu.
National's Bay of Plenty candidate Todd Muller criticised Mr Cunliffe.
"From my perspective, I think it's deeply hypocritical of David Cunliffe. He has spent the last two to three months shouting from the rooftops for the resignation of Maurice Williamson and Judith Collins and now we find out he is closely involved with this individual and has been advocating for him."
Asked if Mr Cunliffe should resign, Mr Muller said: "I think these are the tough questions that he's going to need to ask himself and the Labour caucus should be asking about him."
Tauranga MP and National Party member Simon Bridges could not be reached last night and Labour's Bay of Plenty candidate Clare Wilson couldn't respond before press time.