PARIS—Air France-KLM CEO Jean-Marc Janaillac said he will submit his resignation on May 9 after a majority of Air France employees rejected a pay proposal in a staff-wide consultation that had been his high-stakes bid to extract the airline from a costly labor-relations crisis. A series of Air France strikes–13 one-day walkouts in recent weeks–have cost the company at least €300 million ($359 million). Janaillac launched the consultation in April in a bid to break the ...