In a postal ballot 80.9 per cent voted to continue striking until Friday 26 September, the SNPL union announced on Saturday, reporting a “historic” tournout of 73.71 per cent.
Another union, the Spaf, on Friday extended its strike call for a further two days.
Air France said that, with 65 per cent of pilots on strike on Sunday, it would have to cancel 62 per cent of its flights on Sunday, compared to 55 per cent on Saturday.
The unions have accused the company of playing down the number of strikers.
Services of French airports were badly hit at the weekend, Marseille seeing 81 per cent of flights cancelled on Saturday and Lille cancelling all flights on Sunday.
The SNPL has asked for a meeting with Prime Minister Manuel Valls, who called on them to end their strike on Friday.
Unions believes the company wants to relocate jobs on the low-cost arm Transavia to countries with worse wages and conditions.
Air France accuses the unions of not wanting to negotiate.