AUCKLAND — Air New Zealand is warning passengers of a possible employee strike on the busiest travel day of the year.

The Aviation and Marine Engineers Association (AMEA) and E tū, which represent almost 1,000 aircraft maintenance engineers, aircraft logistics and related staff, notified Air New Zealand on Friday of a planned strike for Dec. 21.

According to the airline, nearly 42,000 customers have booked domestic and international flights on this day.

At the heart of the dispute are pay wages; earlier this year, union members rejected Air New Zealand’s offer of a 2% pay rise in the first year of the agreement, followed a 3% rise over the following 18 months.

Members also rejected a proposal to standardize overtime pay to 150% of regular pay rate and a corresponding $6,400 one-off payment to address the change in rate, reports Reuters.

The airline said the average income of the workers planning to strike is NZ$115,000 (approximately Can$105,000), more than double the average wage in New Zealand.

Both sides have agreed to mediation on Monday with hopes of reaching an agreement.