mean business

US /miːn ˈbɪz.nɪs/
UK /miːn ˈbɪz.nɪs/
"mean business" picture
1.

to be serious and determined about what one is doing or saying

:
When the boss walked in with that look on his face, we knew he meant business.
The new security measures show that the company means business about protecting its data.