Qantas has confirmed it asked police to drop an investigation of threatening letters written to airline chief Alan Joyce at the height of a heated industrial dispute.

Mr Joyce and other Qantas executives were subjected to months of abusive letters, some containing death threats.

There were also allegations that some workers who refused to join strike action had their cars vandalised.

A Qantas spokesman on Wednesday said the airline had asked NSW Police to drop their investigation of one matter.

"Qantas formally requested only one matter to be discontinued - two letters written by the same person in May and a second in August, after he had been spoken to by the police," he said in a statement.

"Both letters contained offensive and abusive language."

NSW Police responded to the threats, revealed by the airline in October, by setting up Strike Force Barrine to investigate.

The strike force had been disbanded, a police spokeswoman said.

NSW Police had referred the matter to the Australian Federal Police, but the AFP said they were not investigating any specific threats and never had.

Qantas has been involved in a long-running industrial dispute, with unions fighting a planned restructure that could see up to 1,000 Australian jobs culled as the airline shifts resources to Asia.