"Whenever agreements are not observed, cabin crew will not report for service," the spokesman for the SNPVAC union, Bruno Fialho, told Lusa.

On Tuesday a spokesman for the SATA group, António Portugal, confirmed to Lusa that the airline had received a formal strike warning for the action from 23 to 26 August. The warning is for Air Açores, which plies routes between the nine islands in the Azores archipelago, and for Azores Airlines, which flies to and from the archipelago.

On Wednesday, the union representative said that two formal warnings were sent, and that "any worker who sees the company agreement and the law being broken will fight", or will "end up in slavery".

Fialho said that the strike is justified not only because of what he said were "daily" breaching of the company agreement, but also the "poor management" at the company and "the way it treats its workers".

He gave as an example SATA "not informing in advance" whether a crew member will be on stand-by or not, which "interferes a lot with people's family life" and which is contrary to the company agreement; according to Fialho, the situation has only arisen because there is a shortage of crew.

Lusa is awaiting a reaction from SATA to the strike warning for the period from Friday onwards.