The Green Party has banned its ministers, MPs and staff from accepting corporate hospitality, such as free tickets to events unrelated to work.
Co-leader James Shaw said the party wanted to counter the influence of money in politics.
"There's no reason why big wealthy corporates should have better or more access to politicians than those organisations who can't afford to shout free tickets to the rugby or a corporate box at the tennis," he said.
"It also gives wealthy corporates an advantage when it comes to influencing our country's decision-makers."
MPs often considered corporate hospitality a perk of the job, but Mr Shaw said it was not essential to the role.
The Greens will also start proactively releasing ministers' diaries to show who they've met with and why.
"Transparency is a hallmark of any functioning democracy, and the Green Party will continue to aim to uphold that, in Parliament and in government," he said.
Mr Shaw would not say whether other parties in government should follow suit.