The aviation unions have slammed Air New Zealand for releasing "misleading information" about planned strike action by its engineers.

Air New Zealand engineers are planning to strike on December 21 - the busiest travel day of the year, putting Christmas travel plans at risk for tens of thousands of travellers.

Savage, the aviation spokesman for E tū, said engineers and logistics workers had voted to issue strike notices in responses to Air New Zealand's demands for cuts to their conditions.

"This is not just about pay. It's about repeated proposals by the airline weeks out from Christmas to pay them less than colleagues who have already settled and to cut into key conditions, including overtime rates.

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"This affects line and hangar engineers, but also store workers and aircraft cleaners, who are covered by the same document and who are struggling to get ahead," he said.

"Our members feel under-appreciated and under attack. The ballot results show an overwhelming resolve to take action to defend themselves."

Savage said no one wanted to disrupt people's Christmas plans.

"..but Air New Zealand has taken an unnecessarily aggressive approach."

Savage said unions had agreed to mediation talks on Monday to try and resolve the dispute and avert the strike action.

More than 970 engineering members of E tū and the Aviation and Marine Engineers Association voted 95 per cent to strike, at meetings in Auckland, Wellington and Christchurch this week.

Savage said Air New Zealand had very high union membership, though strike action was extremely rare.

"Aviation workers don't make these decisions without good cause. In aviation, there is a constant downward pressure on costs driven by airlines. The result is a race to the bottom on wages and conditions," he said.

"We will be in mediation with Air NZ Engineering management first thing on Monday and will carry on bargaining in good faith in the hopes of reaching a deal," he said.