Nine out of ten unions issued a joint statement saying it was “inconceivable that the Air France company, French since 1933, falls into the hands of a foreign executive whose candidacy is being promoted by a competitor”.

The statement appeared to be referring to Delta Airlines, the US airline which owns 8.8% of the capital of Air France-KLM, the parent group formed out of the merger of Air France and KLM of the Netherlands in 2004.

The union statement, which said the new boss needed “intimate knowledge… of the French social model”, said that the board was expected to hold a teleconference on Thursday to discuss the nomination.

The Franco-Dutch airline has been searching for a new boss since Jean-Marc Janaillac resigned in May, having gambled his job on getting Air France staff to accept a new pay deal after months of strikes.

Smith is Air Canada’s chief operating officer who led labour negotiations with pilots’ and flight attendants’ unions ahead of the launch of low-cost operator Air Canada Rouge.

Such experience might come in useful at Air France-KLM, which has suffered months of disruptive and costly strikes by French staff demanding better salaries.

He was tipped to emerge as the new boss of the airline by France’s leftwing Liberation newspaper on Wednesday.

Air France shares have plunged more than 35% since the start of the year, although they have stabilised since Janaillac’s departure.

The group this month estimated the cost of the 15 days of French strikes between February and June at 335 million euros ($391 million).