thin edge of the wedge

Idioms  

1. A minor change that begins a major development, especially an undesirable one. For example, First they asked me to postpone my vacation for a week, and then for a month; it's the thin edge of the wedge and pretty soon it'll be a year. This term alludes to the narrow wedge inserted into a log for splitting wood. [Mid-1800s]

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Example Sentences

Rewriting, oh pardon me, repurposing Roald Dahl's books is just the thin edge of the wedge.

From Salon

Some see it as the thin edge of the wedge when it comes to civil liberties.

From BBC

For Muslims, the citizenship law is “the thin edge of the wedge,” said Hasan.

From Washington Post

One unhappy doctor tells the Daily Mail assisted dying is just "the thin edge of the wedge", but campaign group Dignity in Dying welcomes the poll.

From BBC

Lithwick: So this is the thin edge of the wedge.

From Slate