In September, nine NSW firefighters working in light duties roles were informed by letter that their services were no longer required.

Two of those firies are attached to Wollongong Fire Station.

Outraged by the sudden "sackings", the Fire Brigade Employees Union reacted by pulling relieving firefighters out of stations with worker vacancies, leaving some stations short-staffed.

As a result, 25 fire stations across the state were temporarily closed on October 20.

The matter is before the Industrial Relations Commission (IRC).

Mr Mullins yesterday told the Mercury he did not approve of the way the nine affected firefighters were contacted.

"I have to say I wasn't happy with the handling of it initially … [it] could have been handled better," he said.

"We've had a restructure in our human resources area, letters went out that gave an indication people were going to be terminated and it was really to say, 'look we need to talk to you'.

"My preference would have been, rather than letters, they would have been spoken to and I've made sure that that won't happen again."

He said FRNSW had agreed on the request of the IRC to take no further action until November 25, which the affected light-duties firefighters had believed to be their termination date.

"I can give an ironclad guarantee that that's not the date people will be told they no longer work with us," he said.

"We'll be working with individuals if they want to stay with the organisation, trying to find substantive positions that they can fill suitable to their particular disabilities."

However, he said the service also had an obligation to manage its workforce.

"We can't just keep everybody who's unfit to be on a fire truck," he said.

"A lot of the people concerned actually have opted for medical retirement, they're quite happy to go, but some aren't and we need to deal with those individually."