A Palmerston North sushi shop has been fined, after undertaking the kind of activity a judge says puts workers at risk of exploitation.

E & C World Ltd, trading as Sushi House, was convicted in the Palmerston North District Court on Tuesday of employing an illegal worker.

The company was also fined $4200, for actions Judge Gerard Lynch described as "brazen".

According to the summary of facts, the illegal worker was a man who had been given a work visa in September 2010, but not to work at Sushi House.

His visa expired in 2011, and a deportation notice was issued when his applications to renew his visa were declined.

But he managed to dodge authorities, and got himself a job at Sushi House in September 2014.

The company's director, Eun Ju Lee, did not provide the man with an employment agreement.

The man worked there until June 2015, when he was found and deported.

Lee admitted to the Ministry of Business, Employment and Innovation that she paid the man cash, which meant he did not pay income tax.

The four other people who worked for Sushi House all had employment agreements, had gone through checks to ensure they were legally able to work in New Zealand, and contributed income tax, she said.

The judge said the offending was not elaborate, but was still determined.

Not paying income tax was a cost to the country, and could give the man a competitive advantage over those who did pay tax, the judge said.

However, the man's safety was something the judge was especially concerned with.

A person working illegally would want to stay under the radar.

That mean they would be at risk of being exploited, through poor working conditions or low wages, by bad employers, the judge said.

From a starting point of a $6000 fine - the maximum penalty available was a $50,000 fine - the judge made discounts for an early guilty plea and the company's previous good conduct.