New Zealand's largest union has been forced to pay $5000 for unfairly firing a sick Wellington worker.

In a decision released this morning, the Employment Relations Authority found the Public Service Association unjustifiably dismissed Mary-Anne Kindell on September 23, 2011.

The association is New Zealand's biggest union, representing 58,000 public sector workers.

The authority found the association had not given Kindell an opportunity to respond to the dismissal or adequately determined whether she could return to work.

Kindell had worked at the association's Wellington office since 2005, but was dismissed after several extended periods of sick leave on pay, which included being hospitalised eight times.

Before dismissing her, the association made several attempts to assess whether Kindell could return to work, most of which never took place following disagreements.

But the authority said the association should have tried harder before dismissing Ms Kindell without assessing whether she could return to work.

"A fair and reasonable employer could have investigated better by persevering to engage Ms Kindell and assemble all relevant information from the appropriate medical sources before making a final decision."

The authority rejected Kindell's compensation claims for lost wages because her sickness made doubtful as to whether she would have been able to return to work.

Kindell also claimed her poor health was a result of the unhealthy damp office, a claim the authority rejected.

- © Fairfax NZ News