Simon, I checked a dozen reports. All agree that the lawsuit stems from a Moslem woman, Samira Achbita, who brought the suit in Belgian court.
In the NY Times coverage of the matter, there is this observation:
“It is a very bold step,” said Camino Mortera-Martinez, a research fellow at the Center for European Reform in Brussels, describing the ruling as a landmark decision, if also a political and pragmatic one. “Recently we have seen the court being much more attentive to the political winds rather than being so legalistic, because of the recognition that the E.U. is at risk of collapse.”
(https://www.nytimes.com/2017/03/14/world/europe/headscarves-ban-european-court.html?_r=0)
Certainly food for thought. I am struck with how Europe has been changing when it comes to civil liberties. What ever happened to "liberté, égalité, fraternité"?