A miner fired for making derogatory Facebook comments about a co-worker wearing a cap with an exceptionally long peak has been awarded $28,000 in unfair dismissal compensation.

The Fair Work Commission found the comments were misconduct but held dismissal was unfair because management failed to disclose that it had relied on a secret report into broader bullying allegations.

The maintenance fitter at CBH Resources' Rasp Mine in Broken Hill had been one of several employees who had liked and responded to a Facebook photo of a colleague wearing a cap with an exaggerated peak.

His comments made from his iPhone at home included "I've seen f--kwits with bigger peaks on their hats" and were allegedly directed at a supervisor who wore similar-sized caps.

When the supervisor saw the posts and complained, CBH Resources fired the fitter for belittling and ridiculing a fellow employee who had been left "broken" and considering quitting.

The fitter claimed his comments were not directed at the supervisor but a group of New Zealand shearers who had worked on his farm and dressed like "rappers" with big peaks on their hats.

But Commissioner Peter Hampton found that explanation was not convincing and held that, given the notoriety of the hat in the workplace, the fitter "at best" knew others would get the reference.

The commissioner considered the Facebook posts were inappropriate and had a sufficient connection with the employment relationship since many of the fitter's Facebook friends were employees.

He also considered the supervisor had been the target of a persistent campaign of bullying, including having grasshoppers pushed into his drink bottle, his locker covered in superglue, and offensive graffiti with explicit sexual references about the large peak of his hat.

But while disciplinary action over the Facebook posts was warranted, the dismissal came undone after CBH unwittingly disclosed it had partly relied on a confidential report that found the fitter's behaviour was having a negative effect across the workplace.

Since the report was never put to the fitter for a response, the commissioner found there was "significant procedural unfairness".

"[T]hat injustice is likely to have made a difference to the fairness of the dismissal," he said.

He ordered the mine pay the fitter $28,471 in compensation, after making deductions for his misconduct and finding reinstatement was inappropriate.

Correction: This article was changed to reflect the fact the supervisor was not the mine worker's boss but his peer.