Using maximum power, everyone is on strike (3-3)
I believe the answer is:
all-out
'using maximum' is the definition.
'all-out' can be an answer for 'maximum' (I've seen this in another clue). I am not certain of the 'using' bit.
'power everyone is on strike' is the wordplay.
I cannot quite see how this works, but
'everyone' could be 'all' (all people) and 'all' is found in the answer.
'on strike' could be 'out' (I've seen this before) and 'out' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for all-out that I've seen before include "Using every effort - everybody exit" , "Whole-hearted (effort)" , "Using full strength or energy - nobody home?" , "Using every resource" , "Nobody home, at top speed" .)