Take heed outside parking by trade union (7)
I believe the answer is:
capture
'take' is the definition.
(capturing is a kind of taking)
'heed outside parking by trade union' is the wordplay.
'heed' becomes 'care' (I've seen this in another clue).
'outside' is an insertion indicator.
'parking' becomes 'p' (abbreviation on road signs).
'by' means one lot of letters go next to another.
'trade union' becomes 'TU' (abbreviation for trade union).
'p'+'tu'='ptu'
'care' enclosing 'ptu' is 'CAPTURE'.
(Other definitions for capture that I've seen before include "Take (eg, chess piece)" , "Take opponent's piece (chess)" , "Take prisoner" , "Collar" , "Ensnare" .)