Staff of Jardine Aviation Services are threatening to take industrial action unless the firm improves their pay and working hours.
The employees union - which represents about half of the staff at the ground-support services firm - claims many of its members work long hours and shift patterns. In the most extreme case, it says a worker was rostered on for 28 days without a break.
The union's secretary-general, Wong Yu-loy, said it had held three rounds of talks with Jardine Aviation management over the past nine months without seeing any movement on its concerns. He said the union had waited long enough.