From
Nu.nl.
In short:
KLM has a policy that states that the minimum length of hair has to be 1 centimetre. As her hair length was 2 millimetres she got laid off.
According to the article before 2007 they stated that her hair was too short, but they did not make a fuss out of it. Only from then did they find it offensive.
Interesting fact from the judge:
De Haarlemse kantonrechter stelde dat het bijna kaalscheren van hoofdhaar bij vrouwen maatschappelijk niet algemeen aanvaard is en stelde de luchtvaartmaatschappij in het gelijk.
According to the judge it is not sociably accepted behaviour for women to shave their head bald and ruled in favour of KLM.