Might want to read the article and not just the headline.

A pay rise had been agreed with the Spanish union, CCOO, and it applied to all flight attendants regardless of what union they belonged to. But another Spanish union - Union Sindical Obrera - won a court case in March to nullify the deal. … The union said it objected to the original agreement because those at the table negotiating were not authorised to do so for its members and “legally couldn’t sign that kind of agreement”.

The union has withdrawn from this agreement, via the courts, because their position is that the negotiators didn’t have the authority to sign agreements for their members. So their members are not a part of this agreement, and owe back the additional money they were paid as part of this agreement.

lol no