Air France-KLM booked a net loss of €198 million in 2014, the Franco-Dutch group said in a statement.
"During the second half of 2014, activity was affected by a 14-day strike by Air France pilots, which had an estimated negative impact of €425 million on the operating result," the statement said.
Without the impact of the strike, the firm would have made a net profit of €296 million, up from €130 million last year.
The pilots went on strike over the firm's bid to expand its low cost operation Transavia France.
They feared the plan could force well-paid Air France crew into penny-pinching Transavia jobs, and that the low-cost carrier might be used to take over Air France routes.
Total turnover at the airline in 2014 was €24.9 billion, a drop of 2.4 percent compared to last year.
Under a restructuring programme, Air France-KLM already cut 8,000 jobs — roughly 10 percent of its workforce — in the three years to the end of 2014 through a voluntary departure scheme.
"The economic environment has significantly changed because, after several months of stability, the oil price and the euro has declined appreciably, which changes our own parameters significantly," said chief executive Alexandre de Juniac.
Investors however, were not impressed.
Air France stock went into a tailspin at the opening of the market, dropping more than four percent.