A Channel Island airline is expected to announce whether travellers will have to pay an increase in passenger duty.
The tax is going up in February by between £5 and £40 and some airlines will charge passengers who booked tickets before the rise was announced.
Flybe said it would make a loss if it did not pass the cost on, so its passengers will be charged.
But Aurigny is still deciding whether to absorb the cost of the increased passenger duty for advance bookings.
The airline said it was considering its position and would let customers know on Monday.
Blue Islands said the change would not affect it, due to its fare structure.
Chancellor Gordon Brown announced the higher air passenger tax in his pre-Budget speech in December.