Grand accommodation for new union member (5)
I believe the answer is:
groom
'new union member' is the definition.
(I've seen this before)
'grand accommodation' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'accommodation' becomes 'room' (eg a hotel room).
'g'+'room'='GROOM'
'for' acts as a link.
(Other definitions for groom that I've seen before include "Curry - husband-to-be" , "Stable hand" , "Tender of horses" , "One at wedding" , "Stable-hand" .)