Dismantled pieces built without union ballot (10)
I believe the answer is:
plebiscite
'ballot' is the definition.
(thesaurus)
'dismantled pieces built without union' is the wordplay.
'dismantled' indicates anagramming the letters.
'without' indicates named letters should be taken away.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'pieces'+'built'='piecesbuilt'
'piecesbuilt' with 'u' taken out is 'piecesbilt'.
'piecesbilt' with letters rearranged gives 'PLEBISCITE'.
(Other definitions for plebiscite that I've seen before include "Public vote" , "Popular vote" , "General vote" , "Referendum" .)