Annoyed a union leader by an unusual step (5)
I believe the answer is:
upset
'annoyed' is the definition.
(I've seen this before)
'a union leader by an unusual step' is the wordplay.
'leader' suggests taking the first letters.
'by' means one lot of letters go next to another.
'an unusual' indicates an anagram.
The first letter of 'union' is 'u'.
'step' is an anagram of 'pset'.
'u'+'pset'='UPSET'
(Other definitions for upset that I've seen before include "Disturb - spoil" , "Disturbed or inverted" , "Unhappy or worried state of mind" , "Distressed - surprise" , "'Disturbed, agitated (5)'" .)