Cleaners converged on Parliament to protest against proposed employment law changes.
Beating red buckets with wooden spoons, they chanted "Hands off 6a".
The Government wants to scrap the clause, which protects low-paid workers when their job is restructured.
The demonstrators, mostly from the Service and Food Workers Union, handed over more than 2000 submissions to the Transport and Industrial Relations select committee on the proposed Employment Relations Amendment Bill.
Parliamentary cleaner Mareta Sinoti told the crowd of around 50 that scrapping the clause would cause "suffering".
"We are cleaners, we work hard at a time when most people are at home with our families," she said. "Few people ever see us at work, but when you come in the morning your offices are clean.
"We work hard on low wages ... part 6a is the only job security we have."
Part 6A ensures the jobs of vulnerable workers - like cleaners and caretakers, laundry staff, or hospital orderlies - are transferred to a new contractor on the same terms if a firm is restructured.
Under the plans, announced in October, businesses with fewer than 20 staff will no longer have to keep on those employees.
Wellington hospital cleaning supervisor Lalopua Sanele said she fought hard for the introduction of the law in 2006 and was "angry" at proposed changes.
"Some of the cleaners here are working two, three jobs ... all these people will suffer. We are also working more hours now, to earn more money to support our family, our kids, especially educating them. The cost of living is far too high than what we get."
She said the protest was her only chance to have "a voice".
"Look at what they are doing, they are trying to cut our rights."
Labour leader David Shearer and Council of Trade Unions president Helen Kelly also addressed the crowd.
Shearer said Labour would repeal the changes if elected next year.
Following the protest, he said there was "very little hope" the Government would listen.
"Why pick on the most vulnerable? It's a pretty mean and insensitive government that has to stick the boot in to the lowest paid workers in our country."
Labour Minister Simon Bridges said the bill would provide greater "fairness, flexibility and clarity" in employment law. However, he said he will listen carefully to submissions and recommendations from the select committee.
- Fairfax Media