〜に（は）あたらない

Meaning

「あたらない」 is written 「当たらない」, meaning "does not warrant." States that something is not worth doing to that extent. A way of gently pointing out that the other person's reaction or assessment is excessive and unwarranted.

Examples

あの努力家なら、合格は驚くにはあたらない。 Given that he is such a hard worker, his passing is no cause for surprise.
小さなミスだから、そう責めるには当たらない。 It is a minor mistake, so there is no need to blame him so harshly.