Air traffic controllers in Spain have called two 12-hour strikes for 26 September and 3 October.
The action, should it go ahead, is likely to hit any flights from Portugal which have to fly over Spain.
The USCA union announced that the strikes would take place between 4am and 4pm GMT on both days.
Union members are protesting against disciplinary sanctions imposed against 61 air traffic controllers in Barcelona who were accused of paralysing air space over the city in June and July 2010. Those four days of protest were said to have stranded 200,000 travellers.
The USCA pointed out that 20 out of 22 labour tribunals subsequently found that the controllers had neither disobeyed their employers nor abandoned their posts.
The union also stated that it was ready to talk to air navigation management.
