the thin end of the wedge
idiomPart ofthin
the thin end of the wedge — idiom
1. A small action or event that is the start of something much worse.
1.idiom
Definition
A small action or event that is the start of something much worse.
Example
The new fee is the thin end of the wedge for library services.
Many see the ban as the thin end of the wedge for free speech.