Workers organised to run in short jacket (5)
I believe the answer is:
tunic
'jacket' is the definition.
(I've seen this before)
'workers organised to run in short' is the wordplay.
'workers organised' becomes 'TU' (abbreviation for trade union).
'to run' becomes 'nick' (nick can mean to run quickly).
'in short' means to remove the last letter.
'nick' with its last letter taken away is 'nic'.
'tu'+'nic'='TUNIC'
(Other definitions for tunic that I've seen before include "Shift" , "Military uniform" , "Simple garment" , "Schoolgirl's dress" , "Clobber" .)