Maurice Williamson lobbied three consecutive immigration ministers on changes to the business migrant scheme sought by Donghua Liu and arranged and attended the meeting between current minister Michael Woodhouse and the wealthy businessman last year.
Mr Liu, who was granted citizenship against official advice after support from Mr Williamson - hired professional consultants to lobby the Government to lower the $10 million investment threshold for non-English speaking business migrants.
A spokeswoman for former Immigration Minister Jonathan Coleman yesterday confirmed Mr Williamson lobbied him over changes, but Dr Coleman told him he "felt there wasn't a need for any further changes to existing policy".
A spokesman for Nathan Guy who was Immigration Minister in 2012 said he had "regular discussions with his colleagues on all kinds of issues" but "we don't keep records of every conversation he ever had".
However, an April 2012 letter to Mr Guy from lobby group the Construction Development Alliance, of which Mr Liu was a member, refers to its meeting with him and his "suggestion of possible third category" within the Business Migrant Scheme with the lower investment and language thresholds.
But Mr Guy's spokesman said the idea of a new third category had been around for "a number of years".
"Nathan occasionally discussed it with different people but never committed to progressing it further."
Immigration Minister Michael Woodhouse said this week that Mr Williamson had lobbied him on the issue and his spokeswoman yesterday confirmed Mr Williamson arranged his meeting with Mr Liu last year.