Rumour of underground workers and those unable to vote (6)
I believe the answer is:
minors
'those unable to vote' is the definition.
(only adults can vote in elections)
'rumour of underground workers' is the wordplay.
'rumour of' indicates a 'sounds like' (homophone) clue.
'underground workers' becomes 'miners' (people who work underground).
'miners' sounds like 'MINORS'.
'and' is the link.
(Other definitions for minors that I've seen before include "They're under-age" , "Young people" , "They're too young to vote" , "They are legally under-age" , "could be little ones" .)