Air France stewardesses, furious at being ordered to wear headscarves in Tehran, say they will refuse to fly to the Iranian capital when the airline resumes the service later this month.
Female members of flight crews have been ordered to cover their hair once they disembark in Tehran and unions are demanding that the flights be made voluntary for women.
The resumption of a thrice-weekly service between Paris and Tehran, planned for April 17 after an eight-year break, follows a thaw in relations since Iran agreed to dismantle large sections of its nuclear programme.
Iranian women have been forced by law to cover their hair or face stiff fines or even imprisonment since 1979.
In France, however, public signs of religion have been frowned upon since a 1905 law separated church and state.
Flore Arrighi, head of the UNAC flight crews' union, said: "It is not our role to pass judgment on the wearing of headscarves or veils in Iran.
What we are denouncing is that it is being made compulsory. Stewardesses must be given the right to refuse these flights."
She added that female staff were entitled to exercise their "individual freedoms".
However, a company spokesman pointed out that other airline staff are obliged to comply with Iranian rules and that "tolerance and respect for the customs of the countries we serve are part of the values of our company".
In Saudi Arabia, stewardesses must wear the "abaya", a long robe that covers the body but, unlike Saudi women, are not compelled to wear face veils.