Labour wants trade unions excluded from a potential lobbying register and blames the MP who drafted the plan for including them in the first place.

Green MP Holly Walker's member's bill would require those who lobby politicians to be registered and adhere to a code of ethics.

It passed its first reading with unanimous support from all parties, but Labour has since put forward an amendment that would exclude trade unions.

The unions are major backers of the Labour Party.

Despite Labour's stance, the Greens are confident the bill can pass through Parliament with the support of National and other parties.

Ms Walker told a select committee yesterday that the bill was drafted too widely and she expected it to be changed during the parliamentary process.

However, she did not believe trade unions should be excluded altogether. Rather there was room to close other loopholes so small and non-profit organisations were not unfairly burdened.

"We need to have transparency about who has access and influence in that system. We think the public has a right to know who's influencing members of Parliament and on which issues."

The lobbying register also had to be practical and fair, she said.

Labour MP Trevor Mallard said the bill was a "bad piece of work" and should have been tidied up before going to select committee.

It would currently capture a union official who rang him to help with a constituent's housing problem, or a foodbank that wanted assistance getting a client welfare entitlements, he said.

Labour MP Ruth Dyson said the New Zealand culture was different from its foreign counterparts and easy access to politicians was part of that.

"People stop us in the supermarket and give us an earful of their view . . . It takes me a long time to do shopping and I love it."

People had a right to have a say and she was concerned the bill could intimidate them and stifle debate. "We have those paid lobbyists. We know who they are - New Zealand is a village."

National Party whip Michael Woodhouse said trade unions were influential lobbyists.