Unions are hoping for a turnout of thousands at rallies in the three main centres today against law changes they describe as the biggest labour reform in 20 years.

A batch of changes introduced in Parliament this week would extend a 90-day trial period without normal legal protections to new employees in firms of all sizes, make unions get an employer's consent before entering a workplace, let employers demand doctor's certificates for workers taking even a single sick day and let workers trade in one week's annual holiday for cash.

It would also make it harder for sacked workers to win compensation by subtle changes of wording and a clear statement that a dismissal can't be held to be unjustified solely because of "minor or technical" defects in the process.

Council of Trade Unions president Helen Kelly said the biggest threat to workers came from the package as a whole rather than from any single part of it.

"When you put things like sick leave and 90-day trials together, you get trouble," she said.

"When you put union access to workplaces into that, that means people are being required to prove sick leave or sign 90-day agreements and can't get access to union advice ... this is the most major labour reform in 20 years."

She said the rallies at 1pm today in Auckland, Wellington and Christchurch, and tomorrow in Dunedin, would be just the start of a campaign that would go on until the proposed law changes were withdrawn or repealed.

"There will be further rallies all over the country, and more strike action and more videos. I intend to go to every provincial town."

The campaign has focused so far on the 90-day trial period, which was promised in the National Party's 2008 election policy as a "voluntary" option for new employees and employers with fewer than 20 employees.

It was implemented as promised from March last year.

Workers hired under the 90-day law can be sacked with no rights to compensation for unjustified dismissal, although they still have other legal protections such as the right not to be discriminated against.

A Labour Department evaluation found that half of the small employers who hired new workers up to May this year used the trial period, and that 40 per cent of employers who used it said they would probably not have hired the people they hired without it.

There was no evidence that employers used the trial period as intended to hire people with "disadvantages", except possibly for young people. Ten per cent of those hired under the scheme were first-time workers and 43 per cent were aged under 25.

Almost a quarter (22 per cent) of those hired were fired during the 90-day trial, mainly for poor performance or attitudes.

"There is no evidence linking this 90-day trial to any job creation," Ms Kelly said. Opening it up to all employers would expose far more people to working without the usual protections.

But Employers and Manufacturers Association advisory services manager David Lowe said the scheme gave employers "the confidence to hire sooner rather than later".

"It's not necessarily a difference between jobs being here and not being here. It's about timing," he said.

Labour Minister Kate Wilkinson said most other developed countries had longer trial periods.

"The Australian Labor Party has introduced a trial period of 12 months or six months, depending on the business. The feedback we've had is that three months works well," she said.

"I think the unions are over-reacting. If people want to take part in these rallies they should have a look at the bills and see that the changes are thoughtful, moderate, pragmatic and, above all, fair."

Meal breaks bill
* Removes fixed 10-minute and half-hour breaks, allows flexibility.

Employment Relations Bill
* Extends optional 90-day trial for new employees to all employers.
* Requires employer consent for union access to workplace; consent cannot be withheld unreasonably.
* Ends compensation for dismissal where employer makes only "minor or technical" mistakes.
* Lets employers communicate directly with workers during collective bargaining.

Holidays bill
* Lets employers require doctor's certificate for even one day's illness, at employer's expense.
* Lets employees request cash instead of fourth week's leave.
* Allows transfer of public holidays to other days by agreement.

Protest rally
* Queen Elizabeth Square, lower Queen St, Auckland, 1pm today.

Fijian carpenter Basa Jal owes his job - and his New Zealand residence - to the 90-day trial period for small employers.

Mr Jal, 47, came here with his wife and 20-year-old daughter in April "because there are no jobs in Fiji".

"It was difficult to get a job," he said. "They were asking for a work permit, and at the time I was on a tourist visa."

Finally Sean Robertson-Welsh, who owns New Zealand's biggest fencing supplies company, Effective Fencing in Penrose, agreed to give him a job under the 90-day trial law, and support his application for a work permit.

"I wouldn't have taken him without the 90 days," Mr Robertson-Welsh said.

Four months later, Mr Jal has survived the trial and plans to apply for permanent residence.

"It's good work and good money, better than Fiji," he said. His wife has found a job in a chicken factory. Their daughter is at Aorere College and plans to go to Manukau Institute of Technology next year.

Mr Robertson-Welsh, an English immigrant who bought the company in 2008 after running a similar business in Britain for 15 years, is a bitter opponent of the current employment laws allowing sacked workers to seek compensation for unjustified dismissal.

"It's so bloody archaic here. I've never seen anything like it," he said. "I've been in the Employment Court seven times in three years. In Britain I was in business 25 years and never went to the Employment Court once, which shows you the culture.

"[Here] I'm on first-name terms with the buggers at the Employment Court."

Six months after he bought the company he hired one man who turned out to be "a serial offender", yet had to "manhandle" the man's father off the property when he came threatening a court case. Then police offered to give the man diversion.

"I went berserk. I said I need a conviction to win in the Employment Court," Mr Robertson-Welsh said. "It's like I've bloody landed on Mars." Other new workers turned out to lack the skills which they had claimed on their CVs.

"I got to the point where I was terrified to employ someone else," Mr Robertson-Welsh said. "It was good for us when that 90 days came in."

He was able to use the trial period because he has only 20 direct employees, although he also has about 35 self-employed contractors and supplies fencing materials to most of the big roading projects around Auckland.

He hired Luke Edmonds, 30, as a fabricator/welder in the first week the new law was in force. Mr Edmonds was happy to get the job under the 90-day law because it offered "a different line of work".

"It was fine," he said. "In this line of work it's hard to get a job because it's hard to get your foot in the door. Since it got the 90 days, they let us come on board."

Lisa Stoneham had never worked in telemarketing before she was hired in November by ventilation company HRV in Wellington.

"What attracted me to the job was the stable hours, which meant a stable income so I could easily support my 2-year-old daughter," she says.

She had three days of training, then plunged into cold-calling members of the public. The target was for each telemarketer to make 20 appointments for sales people to meet potential customers, and for five sales out of those appointments.

"I got five or six appointments, but I had four sales, so I was bringing in the sales," she says.

"On the eighth day of working, I felt I was finally starting to get the hang of things. Then, towards the end of my shift, the manager gave me my week's notice, firing me.

"It was a massive blow to my confidence and my self-esteem. I had never been fired before."

The manager told her he did not have to give any reason for dismissal under the 90-day trial law and advised her to ask for the reasons in writing.

Ms Stoneham, now 24, did apply in writing, but has never heard back. She is now on the domestic purposes benefit and doing a pre-trade electrical course at Weltec.

"I don't ever want to work under the 90-day bill again, even if I was offered my dream job," she said.

In Auckland, Joanne Bartlett, now 21, was also mystified when she was fired by Burger Fuel in Mission Bay two days before the end of her 90-day trial period in April.

"I have a really strong work ethic. I would go over and above what anyone asked me to do," she said.

However, a few days before she was sacked she had been asked to come back to work half-way through her break.

"It was a misunderstanding. I questioned it. It was a couple of days before I lost my job, maybe that's the reason," she said.

She asked why she had been sacked and was told that "they didn't see me long-term in the fast-food industry".

In fact she has a diploma in culinary arts and was desperate to get into the food industry somehow. "I've been searching for a job ever since. I've had a few interviews, but I'm on the unemployment benefit," she said.

"I'm sort of going downhill. I try to not let what happened at Burger Fuel affect me, but it does because I don't have a job and feel shitty about myself because of that."

Unite Union's "utu [revenge] squad" staged a picket outside Burger Fuel yesterday to protest Ms Bartlett's dismissal.

"If the Government takes away workers' rights to use legal means to protect themselves from unjust actions like this, then workers have to go back to the tradition of direct action as the only way left to support workers like Joanne," said Unite's Mike Treen.