Unions will be legally bound to carry out a secret ballot to approve strikes after a bill sponsored by National MP Tau Henare was approved by one vote in Parliament.
The private member's bill passed its third reading this evening with 61 votes in favour and 60 against.
Mr Henare, a former organiser for the Clerical Workers' Union, introduced the bill to allow members to make a vote on striking without pressure or intimidation from bosses.
"It is about making a decision without the sword hanging over the top of you.
"Is it too much to ask for that workers get the right when they are asked to withdraw their labour to do it in such a way that is secret to them?"