CityJet pilots are planning to walk out for "an unlimited period" in protest at Intro Aviation's proposed acquisition of the Air France-KLM regional subsidiary.
In a joint statement, unions SNPL France ALPA and UNAC complain that the sale agreement contains no provision for investment or capital contribution, and that charter contracts would be cut in half.
The deal "clearly threatens the employment of pilots in France", say the unions, adding that it "is similar to a bankruptcy organised by Air France and a dismantling of the company left in the care of the buyer".
The pilot representatives are seeking an agreement on social terms, and work stoppages are to begin on 2 January.
Earlier this month, German investor group Intro made a firm offer to acquire both CityJet and Air France-KLM's Belgian unit VLM.
"This offer provides for ongoing commercial co-operation with Air France as part of a new industrial plan," said Intro. "Employee representative bodies of the various entities will be informed and consulted. The transaction is expected to close in the first quarter of 2014."
Turnaround specialist Intro has acquired and subsequently sold a number of airlines, including German charter carrier LTU and former British Airways subsidiary Deutsche BA.
CityJet generated revenues of $271 million on 1.5 million passengers in 2012. The Irish carrier has been a wholly owned Air France unit since 2000.
Air France-KLM announced in February it had put CityJet up for sale after an overhaul of the group's regional operations.