Unions representing airport security staff are warning of huge delays and cancelled flights at airports after lock-out notices were issued against their members.

E Tu and the Public Service Association said the Aviation Security Service's decision to lock out employees later this month was an irresponsible move which would inconvenience travellers.

Negotiations have broken down on pay talks between the parties, which have been going on for about a year.

The unions said it was unlikely that the Civil Aviation Authority would be able to provide full security coverage during the lock-out, which will take place between July 20 and 27.

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"This is an extraordinary step and one that gravely concerns us," E tū National Organiser Kelvin Ellis says.

"The lockout notices cover eight days including the final days of the school holidays, and they also affect Queenstown and Dunedin airports - which are not part of our industrial action."

Aviation Security Service Group Manager Karen Urwin said they thought that their pay offer was fair, but if a mediation meeting on July 15 did not go well, they had contingency plans in place for airports.

"We have staff who are on individual employment agreements. We have staff in management positions and we have staff who are doing other roles across the sector who are all qualified to screen."

Ms Urwin said they're aware it will be the school holidays and families will be looking to get away, so they'll do everything they can to minimise disruption.

Prime Minister John Key has said an option is to bring in other agencies like Police or Customs to do the job.