Labor is accusing NSW Premier Barry O'Farrell of breaking the ministerial code of conduct, after he admitted to a "dropping in" on a meeting attended by businessman Nick Di Girolamo before he was on the government's official list of lobbyists.
Mr O'Farrell has been under pressure from Labor to reveal whether he met with Mr Di Girolamo about the Wallarah 2 coal mine in the state's Central Coast.
The premier says on February 28, 2012, he "dropped in" on a meeting with South Korean company, Kores, which had been pushing for the mine's approval.
Mr O'Farrell says he was there for only five minutes to say "hello" to the company's president and to apologise for not meeting him earlier.
Former Energy and Resources Minister Chris Hartcher and Mr Di Girolamo were also at the meeting. Both men are now the subject of an Independent Commission Against Corruption (ICAC) inquiry.
Mr O'Farrell on Thursday revealed that at the time of the "drop-by" meeting, he did not know that Mr Di Girolamo was not on the government's lobbyist register.
It was only after media inquiries made to Mr O'Farrell's office a year later that his staff realised Mr Di Girolamo wasn't on the register at the time of the meeting. Mr O'Farrell says Mr Di Girolamo appeared on the lobby list in March 2012.
"Even though he presented himself as on the register, he wasn't when we checked a year later," Mr O'Farrell said during question time on Thursday.
Opposition Leader John Robertson says the premier "clearly" breached the ministerial code of conduct.
"By his own admission, Barry O'Farrell has allowed himself to be lobbied by a Liberal Party donor and personal friend who wasn't a registered lobbyist - a clear breach of the ministerial code of conduct," he said in a statement.
The premier says after his office realised Mr Di Girolamo was not on the list, Mr O'Farrell's then-chief of staff "immediately" informed the director-general of the Department of the Premier and Cabinet.
"The director-general wrote to the parties including the then minister and Mr Di Girolamo to remind them of their obligations under the code," Mr O'Farrell said.
"I also reminded my staff about the importance of complying with the code at all times."
Mr O'Farrell insists he hasn't had any "private" meetings with Mr Di Girolamo about the mine project.