The problem here is not with Ryanair demanding that the rate of tax ( it was always taxed but at a lower rate ) is increased. That has been done by my fellow Scotsman
a Mr Brown
The problem is that Ryanair always said that sector pay was net of tax, but now that the tax rate is going up they are trying to bludgeon through a deal where that is no longer the case. I.E. they don't take the hit = the pilot takes a cut in pay.
In most airlines it is a big deal, but more so in Ryanair as sector pay/duty pay/ whatever you call it - is a higher percentage of total earnings than in most other companies.