Their restless sleep is interrupted for work (or races) (7)
I believe the answer is:
peoples
'races' is the definition.
(I've seen this in another clue)
'their restless sleep is interrupted for work' is the wordplay.
I cannot quite understand how this works, but
'work' could be 'op' (abbreviation for opus) and 'op' is located in the answer.
an anagram of 'sleep' is 'peles' which is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'or' acts as a link.
Can you help me to learn more?
(Another definition for peoples that I've seen is " Nations, ethnic groups".)