The Civil Aviation Authority (CAA) is being accused of using aggressive tactics in threatening a lockout for airport security staff planning strike action over pay.
Rolling strikes are planned for later in July at Auckland and Wellington airports, but only a ban on overtime at Christchurch Airport.
With a heavily unionised workforce, the industrial action could mean significant delays for travellers on those days.
E tū and the Public Service Association say no staff want to take the action, but they're unhappy with negotiations on the new collective agreement. If the strikes go ahead as planned, it'll be the first industrial action by the security staff in 30 years.
The Government has said other agencies could step in to help during the affected times.
However, the Aviation Security Service (Avsec) has issued lockout notices to union members which would apply for one day during the strike.
It would bar any security staff from their workplace.
That's led to the Council of Trade Unions to call the CAA, which oversees Avsec, "aggressive" and "irresponsible" in their handling of the situation.
"Good employers do not prevent those they employee from coming to work. This is exactly what Civil Aviation is intending on doing by 'locking out' people who have joined together in union to achieve better terms and conditions at work," president Richard Wagstaff says.
"This is the response from Civil Aviation to these working people who are refusing to do overtime, withdrawing their labour for a total of three hours and a putting ban on increased hours of work for part timers.
"I cannot remember such an aggressive act by a state sector employer in the last 30 years."
Mr Wagstaff says the CAA's lockout would create "major disruption" for the travelling public during the second week of the school holidays.
He says the notice is disappointing considering the relevant parties are scheduled for mediation through the Ministry of Business, Innovation and Employment next Friday.