During Budget Estimates on Friday, NSW Labor MP Luke Foley drew the premier's attention to Joseph Tannous' LinkedIn profile.
Joseph Tannous is executive director of the lobbying firm 1st State Government and Corporate Relations, and also a member of the NSW Liberal state executive.
It says Tannous "enjoys constant contact with elected representatives from across the political divide enabling him to attain the desired results for his clients".
Under NSW law, lobbyists are banned from making exaggerated claims about their access to governments, and must keep their business activities separate from any personal involvement in political parties.
The premier objected to Foley's line of questioning after the Labor MP pointed out that Tannous lobbies for Thiess, which last month won an AU$1.15 million north-west rail tunnelling contract.
Tannous also represents Dell Australia, which recently won an AU$455,000 government contract, which wasn't put out to tender, and was the first of two companies to be put on sacked Finance Minister Greg Pearce's AU$93 million procurement panel.
The premier called on Foley to produce any evidence that the deals were dodgy.
"If you have evidence their success has been unduly influenced, then present it; otherwise, you are simply smearing."
Foley asked the premier whether he felt Tannous' claims of access were a breach, and called on him to "punt Mr Tannous from the lobbyist register".
O'Farrell deferred the issue to the director-general of the Department of the Premier and Cabinet, Chris Eccles, who said he would investigate the matter.
"We have the responsibility to review that," he added.
Foley suggested there were seven people on the Liberal state executive who could be termed lobbyists, although the premier claims that there are only three.
Foley asked the premier what would happen to one of them if they claimed they could deliver results because they sat on the executive.
The premier replied: "That's a matter I would potentially refer to ICAC."
He later said he would take advice from Eccles about whether he should refer Tannous to the corruption watchdog.
O'Farrell also made clear his position on lobbyists.
"I have no idea why people waste their money," he said.