slam (on) the brake(s)
1. Literally, to quickly press on a vehicle's brakes to slow down or stop. He slammed on the brakes when he saw the child running into the street. You risk doing your car serious damage if you slam the brake without shifting down the gears.
2. By extension, to slow down or stop something that one is doing. We had to slam on the brakes when we found out investors were pulling out of the company.