First, Lufthansa announced the cancellation of thousands of flights. The company reasoned this with Verdi's strike of ground personnel.
This mainly affects the hubs Frankfurt (FRA) and Munich (MUC) yet also many other airports (Dresden, Berlin, Hamburg etc.). It is expected that the impact on routes etc. will last until Friday. Numbers of around 134,000 affected passengers are circulated.
Secondly, Spanish unions USO and Sitcpla announced a strike period from August until January 2023 (yes, you've read correctly, around five months). The impact is yet to be seen.
Solidarity. Right of collective bargaining and action. That's the heading of article 28 of the EU's Charter of Fundamental Rights. Workers are guaranteed to bargain and to strike for their interests.
A strike always is disruptive. Yet, it is a risk inherent to every business including airlines.
It's time for a reminder of your right's as passengers should you be affected:
I. Your Compensation
First and foremost, you're quite likely entitled to a compensation.
A strike by airline staff – we're talking about a strike that's within the legal limits – is generally considered to be within an airline's control. Verdi's announcement referred to “ground personnel employed by Deutsche Lufthansa AG”. That indicates that it's the airline's own personnel. Consequently, Lufthansa's passengers would be entitled to a compensation.
The European Court of Justice has clearly decided so in the case against SAS (verdict 23.03.2021; case C-28/20):
SAS had denied paying compensation to passengers for flights disrupted due to strikes in 2019. Technically, the airline claimed extraordinary circumstances (art. 5 (3) Reg. (EC) No 261/2004)).
The EuCJ turned down that argument and swiftly so. Strikes "fall within the normal management of [...] carrier's activities"; also, "the employer retains control over events to a certain extent" (EuCJ, para. 29, 35). However, this does not apply to strikes from third-party staff (e.g. strike of air traffic control).
This recent decision also applies to other strikes that have occurred in the recent past, e.g. Lufthansa's cabin crew strike in late 2019.
In short, you are entitled to a compensation if your flight has been disrupted due to a strike by the airline's staff.
II. Alternative Travel
Lufthansa is – per Regulation (EC) 261/2004 – obliged to provide alternative ways of transport. They have tried to rebook.
III. Duty to Care
Lufthansa is obliged to provide you with food and drinks while waiting at the airport. The quantities depend on the situation, mainly the duration of the delay. It might also hand out vouchers to ensure sufficient quantities are provided.
Kindly note that Lufthansa has informed passengers not to come to the airports should flights be cancelled. Chances of getting alternatives in situ are slim if not nought.
IV. Accommodation
Lufthansa also has to ensure accommodation for the duration of the disruption should your alternative only leave the next day. A transfer to a hotel is included.
V. Recommendations for You
The main thing is to ensure sufficient evidence of who canceled or changed what and when. So save all e-mails and take notes of any other communication happening.
You should insist on Lufthansa personnel to make any changes to your itinerary if you want to be on the save side regarding any expenses incurred (or reimbursement) due to the strike. Also, have them book and pay any alternative transport.
Let personnel at the airports hand you written confirmations for any changes or any promises (for vouchers, reimbursements, bookings etc.) made. Exchange contact detail with fellow travelers in the queue.
Claim damages meaning expenses incurred should the airline fail to provide you any of the mentioned relieves (see II. - IV.).
Apply for a compensation or reimbursement of expenses in any way to ensure your chances are being verified.