The rally interfered with today's flights, airline officials said.
In addition to the rally itself, THAI staff refused to move the airline's aircraft from their assigned waiting areas interfering with operations so that the flights of other airlines could not take off or land at the airport.
The protest interfered with luggage handling, forcing the delay of luggage reclamation by almost one hour.
The protesters also called on airline chairman Ampon Kittiampon to resign from his post.
Meanwhile, Transport Minister Chadchart Sittipunt ordered national flag carrier President Sorajak Kasemsuvan to meet with the employees who staged the protest.
He vowed to move against workers who left their duties to join the protest which caused disruption of flights and affected many travellers.
The protest reportedly delayed the flight by 10 to 15 minutes.