Female flight attendants have expressed their opposition to orders from Air France requiring them to wear headscarves and loose clothing in Iran.

The airline is set to resume its Paris to Tehran service on April 17, but a number of flight crew unions are taking a stance against the clothing limitations and headscarf requirements linked to the trip.

The Union des Navigants de l'Aviation Civile (UNAC) has called them "true threats to their dignity" in a letter sent to France's minister for women's rights and families Laurence Rossignal on Friday.

Meanwhile, the Syndicat National du Personnel Navigant Commercial (SNPNC) has said in a statement that they are "an attack on freedom of conscience and individual freedoms, and invasion of privacy".

The union representatives are demanding that working on the Tehran flights be made voluntary for female employees who do not wish to adhere to the restrictive clothing policy and want assurances that it will not negatively impact their pay or schedules.

Currently, workers are being told that they must wear trousers on the flight, and a headscarf and loose fitting jacket when they exit the plane.

The rules had been in place before the Tehran service was cut in 2008 as part of international sanctions due to Iran's nuclear programme.

Flore Ariighi, head of the UNAC, told the Telegraph:

"What we are denouncing is that it is being made compulsory. Stewardesses must be given the right to refuse these flights".

Air France has said:

"Iranian law requires that a veil covering the hair be worn in public places by all women on its territory. This obligation, which does not apply during the flight, is respected by all international airlines which fly to Iran".