To avoid disruption to passenger travel during the planned Sept. 20 strike by about 3,800 union employees, Qantas will use larger aircraft and redeploy staff.

Qantas announced the contingency plans ahead of the industrial action to assure travelers that the air carrier would still fly even if it is bracing for flight disruptions due to the four-hour work stoppage which could affect the airline up to two days.

Among the other measures to be put in place are to consolidate services, deploy management employees to perform operational tasks during the duration of the job walk-off by baggage handlers, caterers and ground staff.

Qantas also said it will publish an updated schedule and contact passengers who would be affected by the strike for the air travelers to make alternative travel arrangements, Qantas Group Executive Olivia Wirth said on Thursday.

The strike on Tuesday will be from 7 to 11 a.m. in most Australian airports. It is expected to affect morning peak hours.

"The union is intentionally disrupting the travel plans of Australians," Ms Wirth said in a statement.

Members of the Transport Workers Union (TWU) are seeking a 5 per cent pay raise and a stop to contract labour. In a ballot conducted by the Australian Electoral Commission the past month, 95 per cent of the union members voted to walk off their jobs because of perception that the Qantas management is stonewalling on enterprise negotiations.

"We're hopeful that Qantas will actually make an offer but in the last number of months they have failed," TWU National Secretary Tony Sheldon told 9 News.

The Tuesday strike would be one of three industrial actions being taken by Qantas workers' unions on the same day. Engineers and pilots of the national flag carrier are also walking off their job over pay and work conditions. Ms Wirth accused the unions of ganging up on Qantas.

The TWU criticized Qantas for spending much on advertising to promote the airline's "new spirit" campaign and making $250 million profit, while shedding 1,000 jobs and planning to relocate key aviation hubs to Asia.

Qantas is negotiating to add more flights to China through five carriers that would have Malaysia or Singapore as base. The expansion is part of the company's bid to obtain a larger cut of the fast-growing Chinese passenger market.