Companies sometimes marching, sometimes standing (6)
I believe the answer is:
orders
This clue is a triple definition!
'companies' is the first definition.
(both can mean a group or association)
'sometimes marching' is the second definition.
(marching orders is a military order)
'sometimes standing' is the third definition.
(as in a standing order)
(Other definitions for orders that I've seen before include "Holy - -" , "Commands and edicts" , "Commands these priests and nuns?" , "Demands" , "Decrees, commands" .)