The Greens have called for lobbyists to be registered, saying the public deserves to know how politicians are being influenced on issues such as Sky City's proposal to build a new Auckland convention centre in return for changes to gambling laws.

Green MP Sue Kedgely today released her Lobby Disclosure members bill, which would set up a register and code of conduct for lobbyists.

"Lobbying is entrenched in our political system, but lobbyists are able to operate in secret and under the radar, in the shadows of our democratic process," said Ms Kedgely.

"The public has no way of knowing who is lobbying their politicians or what they are being lobbied about. There is also no information available on which lobbyists have special access to Parliament granted to them by the Speaker."

Ms Kedgely said there were currently lobbysists "trying to water down the alcohol law reform bill, we know that there are lobbyists working on the code of welfare for hens trying to dilute that, we know that the casino is trying to bring about legislative change for gambling".

Casino operator Sky City yesterday revealed plans to build a $350 million convention centre in downtown Auckland saying it would pay for the project itself but that it wanted the Government to consider changes to gambling laws to allow for extension of it license beyond 2021 and for an increase in gambling machines and tables.

Prime Minister John Key has said any law changes, "will be subjected to a full public submission process".

But Greens co-leader Russel Norman said there was a lack of transparency around the issue that would be addressed by Ms Kedgely's bill.

While there had been a tender process to decide who would build Auckland's new convention centre, "whether parallel to the tender process, Sky City has been meeting with various Ministers or the Prime Minister we just don't know" said Dr Norman.

"In the absence of a lobbying register there is no requirement for it to be public."

Under the Greens' proposal, lobbyists would have to register with the Auditor General's office and file quarterly returns detailing which politicians they'd spoken with and on what issues. That information would be publicly accessible.

The Auditor General would also draw up a code of conduct and any breaches would result in suspension or even fines.

"We believe the public has a right to know who is engaged in lobbying activities that seek to influence public policy," said Ms Kedgely.

"We want to get lobbying out of the shadows and ensure it takes place in as open a way as possible."