It is not compulsory, not VIP either - any person authorised (carte d'access etc) for Strasbourg can a get a ticket in the parli travel office. Not sure why there is only two trains (mon morning and Thurs early afternoon) the cost is quite high I think, although with the cancellation of 6 air charters there is a samll net saving, I understand.

I am just today kicking myself for being disorganised and missing the deadline to get a reservation - means I will be on the slow train next week. Duh