More than two dozen flights were cancelled and thousands of passengers stranded as pilots at Kenya Airways, one of Africa's biggest carriers, began a strike on Saturday, despite the government urging them to call it off.
The strike that began at 6am will affect thousands of business and leisure travellers at one of Africa's most important aviation hubs.
The Kenya Airline Pilots Association (Kalpa) said the carrier's management declined to listen to their proposals on how to resolve their grievances.
"No KQ [Kenya Airways] aircraft has departed Jomo Kenyatta International Airport flown by a Kalpa member from 6am this morning," the union said. "The strike is fully in force."
The national carrier's chief executive officer Allan Kilavuka said pilots had been issued a 24-hour return-to-work ultimatum, after which they will be considered to have absconded from duty.
About 9,000 passengers have been affected so far, he said.
Before the action, the company had called the planned strike unlawful and warned it could jeopardise its recovery from the Covid-19 pandemic, saying it could lose at least 300 million shillings ($2.5m) a day.
A stranded passenger at the airport in the capital Nairobi, who identified himself as Lawrence, said he had arrived at 5am to take a flight to Johannesburg in South Africa but "unfortunately they've just told me that it's cancelled due to the strike".
Other passengers told Reuters early on Saturday that the previous night was chaotic as travellers sought to travel before the strike began. Hundreds of passengers who had arrived in transit were trapped inside the airport as their connecting flights failed to take off, they said.
The pilots union said it would call a strike over a dispute on pension contributions and settlement of deferred pay for its members after a 14-day notice had passed without the airline's management addressing their grievances.
In last-minute talks to avert a strike, Transport Minister Kipchumba Murkomen issued a plea to the pilots union not to go ahead with the industrial action.
Kenya Airways carried more than 8,000 passengers daily in the first half of this year, according to the airline.
— With reporting from Reuters and Bloomberg.