The controversial labour law was introduced in 2011, but Labour spokesman Andrew Little said the case was evidence of the confusion among many employers and workers about how 90-day trials worked.
Martin, from Auckland, was inducted on May 14 last year and signed an employment agreement the next day to work as a researcher and writer about Hardy's products.
The employment agreement allowed for her to be fired on a fortnight's notice if her performance wasn't up to scratch.
It also referred to "employment reviews" that would have to precede any decision on whether Martin met her employer's standards.
On August 2, Martin was fired, with Hardy's emailing her at 3.31pm, saying the sacking was effective immediately.
She was given two weeks' pay.
Authority member Robin Arthur said Hardy's failed to observe good faith obligations to Martin.
Arthur said it was problematic that Hardy's did not ensure Martin signed an agreement before starting work on May 14.
This virtually voided the agreement signed the next day - making it untenable for Hardy's to "exercise the advantages" of the 90-day trial provisions.
An agreement with Hardy's was offered a week before but Arthur said it was "oddly worded" and not signed.
Staff had "concerns" about Martin's ability to work to deadlines and deliver the output Hardy's expected. But these concerns were never "put squarely or plainly" to Martin during her 11 weeks of employment.
"Accordingly, the failure to properly address performance concerns with Ms Martin was an unjustified disadvantage - it was not something that a fair and reasonable employer could have done, even if the trial period provisions had been valid and enforceable," Arthur said.
The authority heard Hardy's brand manager Margaret Hardy accepted Martin was never told her job was at risk. But Hardy said her style was to "nurture, not criticise" so she provided positive feedback to Martin.
The authority decided Martin should be awarded $20,700 for lost wages and $10,000 compensation for humiliation, loss of dignity and hurt feelings.
"One of the problems with the law is, it sends a signal to employers that there are no kind of standards anymore," Little said yesterday. "I expect there are a lot of cases that are probably unlawful dismissals but no one's ever taken any action."
Martin declined to comment.
Her counsel, Don Mackinnon, and Hardy's counsel, Damian Botherway, did not return calls yesterday.