The number of workers seeking help over their poor employment contracts has surged by several thousand in the last five years, community groups have reported.
The Citizens Advice Bureau (CAB) and Community Law Aotearoa said they were now giving advice to up to 12,000 people a year each over employment breaches.
Complaints of unfair treatment, insecure hours, no sick leave, changing job terms and unjust dismissals are all highlighted in a report released by the Citizens Advice Bureau this morning.
Other workers say they have no written contracts and some have been fired after asking for one.
The CAB report said it had dealt with 473 people without any employment agreement in the last six months alone.
CAB social policy adviser Jayne McKendry said the number of people asking for help with employment problems had risen by 40 percent in the last five years.
"One person that came to us had been working for a really long time for an employer, he'd got sick, had some time off... and when he came back, he was told that he was no longer a permanent employee," she said.
Young people and migrants were most vulnerable, Ms McKendry said.
Without contracts, she said, many employers were abusing the 90-day trial scheme or altering hours without notice.
"We have clients come to us who have been aware they had a right to a written employment agreement, have asked their employer for [it] and been sacked on the spot."
She said government agencies such as Inland Revenue and ACC should do more to enforce the rules for employers.
Community Law Aotearoa chief executive Elizabeth Tennet said a lack of contracts was a never-ending problem.
"There are times when employers are deliberately breaching their requirements and it is unfortunate that some vulnerable people are being abused and not receiving their employment rights."
Ms Tennet said the thousands who did approach them and CAB were just the tip of the iceberg.
"Because they are in low-paid minimum jobs they are desperate to keep, they often don't complain when they're not being treated legally correctly."
Council of Trade Unions president Richard Wagstaff said the figures reflected a broken employment system.
"Over the last 10 years we have seen constant erosion of the Employment Relations Act by something like 20 amendments by this government alone, and all of those things have made it a little easier for employers to have their way when it comes to employment relationships.
"We also know it has become common place for employers to have very informal relationships with their staff," Mr Wagstaff said.
He said school leavers needed to learn about the working world, and employers simply should know the law.
Employers and Manufacturers Association chief executive Kim Campbell said the figures were a national disgrace.
"The law requires people to have an employment contract, end of discussion, and employers are obliged to provide them, end of discussion, and someone who doesn't have one is entitled to bring agreements, end of discussion."
All of the groups RNZ spoke to stressed that the Labour Inspectorate - New Zealand's employment watchdog - was grossly underfunded and under staffed.
But Labour Inspectorate national manager Stu Lumsden said it was sufficiently staffed and its strategy was to get the industry to take responsibility.
He said employees could complain about contracts or mistreatment through the inspectorate's contact centre and online.