I have claimed several times and have had legitimate claims refused, which seems to be part of some airlines policy, as they expect you not to take it any further.
My claims have been in and out of Spain where the Government offer a free appeals service. Here is a link, it is in Spanish, so click the translate button if using Chrome.
www.seguridadaerea.gob.es/lang_en/particulares/cancelac_retraso/default.aspx
Under EU law, you're only entitled to compensation if you hear from the airline less than 14 days from the date you're due to fly that your flight is cancelled.
If the airline warned you of the cancellation at least two weeks prior to your scheduled time of departure, you won't get compensation but you'll get a refund.
Is a strike an extraordinary circumstance?
Airlines are not always obligated to offer compensation following a strike because strikes are usually considered to be 'extraordinary circumstances'. These are situations beyond the control of the airline, and can include adverse weather conditions as well as certain strike action.
But when a a flight is delayed or cancelled due to strike action taking place by the airline's own employees (eg. pilots, airline staff), then the airline is required to pay compensation to passengers.
Even sudden 'wildcat' strikes aren't classed as extraordinary circumstances when the industrial action has been called by an airline's staff rather than a third party, such as an air traffic control or a baggage handling strike.
This principle was confirmed by European judges in the German case of Helga Krüsemann and Others v TUIfly GmbH and will be legally binding throughout Europe and in the UK.
It remains the airline’s responsibility to ensure it has contingencies in place to guarantee you still arrive on time.