Revelations have surfaced that death threats have been sent to senior managers at Qantas. The airline's chief Alan Joyce has asked for calm amid the industrial negotiations.

The airline is involved in a continuing industrial dispute which could see more than 1000 staff let dismissed; a planned restructure that the unions are vehemently opposing and fighting tooth and nail.

Having received one of the threatening letters, Mr Joyce has conceded that he does not believe union officials are responsible, however has urged that the tone of the negotiations and communications need to be more conciliatory and 'less aggressive'.

"I absolutely believe that they are calling on their members ... and anybody out there that this is the wrong behaviour and cannot be tolerated," Mr Joyce told Fairfax Radio in Melbourne.

He insisted that both sides of the dispute needed to be more sensible.

"We've asked the union leaders, we've asked all of our people to make sure that the tone is a lot more sensible than it has been," he said.

"I think the rhetoric and aggression has got to this level and I don't think that is good for anybody."

Mr Joyce admitted he was fearing for the safety of Qantas employees, and disappointed that such threats had been made.

"I think it is vile. I think it's cowardly; intimidation and bullying in any workplace ... is something we should not allow," he said.

Transport Workers Union NSW secretary Wayne Forno said he did not believe the union was responsible for the threats.

"There's no place for violence in any industrial campaign. There's no room for acts of intimidation and violence," he told ABC Radio.

Australian Licenced Aircraft Engineers Association federal secretary Steve Purvinas told Macquarie Radio his union was not behind the death threats and had advised members in 2008 not to get involved in intimidation.

"We sent a message again about a month ago to our members, 'Just play it legally' because that's what worked last time.

"For those reasons, I don't think any of our members would be involved in this threat that Alan claims has been sent to his house."

Senior staff at Qantas have had their car windows smashed and homes damaged after refusing to strike being referred to as 'scabs', and Mr Joyce himself received an explicit death threat.

A type written letter, sent to Mr Joyce's home, read in part: "It's coming soon Paddy. You can't even see it!"

"The Unions will fight you ... Qantas is our airline, started & staffed by Australians, not foreign filth like you."

The threats are currently being investigated by police.