how come airlines change taxes on airfare ?

tricia r asked:


I travel alot and I cant believe the taxes they are now charging are even done in a legal manner.. For example

The same airline same seat class may charge $533 Rt to Europe and its is $609 with taxes
then they offer a promo fair same airline same class
for $337 and with taxes its is still $609

How come they can legally play with taxes in this way ?
I understand they must pay for security and airport fees from our tickets taxes but this is a very unfare way and seems fishy

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