Downing tools? That’s impressive (8)
I believe the answer is:
striking
I believe this clue is a double definition.
'downing tools?' is the first definition.
(going on strike)
'impressive' is the second definition.
(similar in meaning)
'that's' is the link.
(Other definitions for striking that I've seen before include "downing tools" , "Remarkable; hitting" , "Hitting or refusing to work" , "Dramatically beautiful" , "Impressive; refusing to work" .)