the thin end of the wedge
(especially British English) an event or action that is the beginning of something more serious and/or unpleasant(不好的事物的)端倪,冰山一角- The introduction of a tax on workplace parking is seen by many as the thin end of the wedge.对工作场所停车征税的引入被许多人视为楔形的细端。
See also thin | end | wedge