Air France cabin crew have called for a three day walkout to coincide with the second batch of British Airways strikes on March 28.
The French unions have come out in sympathy for their UK counterparts, while also protesting over planned job cuts by their own airline.
The run up to Easter could be even more chaotic than expected, with Portugese pilots due to walk out from March 26 to 31.
Unite has also gained support from Teamsters, the transport union in the US, after visiting its Washington headquarters yesterday.
Meanwhile, BA tried to improve the situation by announcing that it would be running more flights than expected during the strikes.
BA claims up to 1,000 employees have offered to stand in for those who strike and expects that number to rise further.
Chief executive Willie Walsh said: “I am delighted by the numbers of cabin crew who have been getting in touch with us to express their disillusion with Unite’s position.”
The airline said it was “pleased” the number of other airlines offering to help fly passengers during the strike had increased from 50 on Monday to more than 60.
It said it would carry 49,000 passengers a day rather than 45,000 during the first stoppage after more of its staff volunteered to work.
Some of the cancelled flights have been reinstated after BA secured more aircraft for the three-day walkout.