It claims that 350 jobs will go in Dublin as a result with another 300 lost in Shannon.
Ryanair is reducing the amount of planes it flies from Dublin from 17 to 16, while the Shannon fleet will be cut from four to three.
This will result in Dublin losing 44 flights a week while Shannon will lose 36.
Ryanair says the winter cutbacks can be reversed if the Government scraps the €10 tax.
It says air traffic has fallen by 11% at Dublin airport in the first five months of the year - a loss of 1m passengers.
Ryanair Chief Executive Michael O'Leary said the cuts would lead to the loss of around 100 Ryanair jobs, 50 at each airport, though those affected could apply for Ryanair jobs elsewhere.
