BEIJING, April 17, 2008 (AFP) - China's civil aviation authority Thursday stripped China Eastern Airlines of some routes and imposed a fine after the carrier's pilots turned around flights in a suspected labour protest.

Twenty-one flights in the southwestern province of Yunnan reversed course just over two weeks ago in what has been widely reported in the state-run press as a protest by the pilots for better work conditions.

The Civil Aviation Administration of China announced the punishment on China Eastern -- the country's third biggest carrier -- in a statement.

'We have fined China Eastern Airlines 1.5 million yuan (215,000 dollars), which will be turned over to the state treasury,' the agency said.

China Eastern was stripped of the right to fly an undisclosed number of routes in Yunnan, with those services to be transferred to other airlines, according to the statement.

The administration called on the airline to uphold air safety, severely punish the people responsible and to continue investigating the reasons behind the incidents.

After the fine was announced, the airline apologised for the incident.

'We again express our deep apologies for the negative influence this incident has had on society and for the inconveniences that it has given to our passengers,' it said.

'The accident has revealed our existing management problems and taught us a very important lesson.'

The original reason given for the flights being turned back was bad weather.

But a preliminary investigation by the CAA that was reported earlier found the weather at all destinations in the province was suitable for landing.

According to the Southern Weekend, unnamed airline pilots admitted the action was a strike to air grievances over salaries paid for the short-haul flights in Yunnan, where landing conditions in mountainous areas are dangerous.

Strike actions are very rare in China, where union activity is strictly controlled by the ruling Communist Party.

Employees in any industry are only allowed to belong to the ruling Communist Party-controlled All China Federation of Trade Unions.

However other pilots appear to have become increasingly bold recently over employment conditions in the heavily regulated industry.

Forty pilots for Shanghai Airlines called in sick at the same time on March 14 in another suspected industrial action.

On March 28, there were long delays for passengers with East Star Air who were trying to fly out of the central city of Wuhan, with reports saying that its pilots were locked in a dispute over working conditions.