[Gockie]

訳にはいかない（用例：そういう訳にはいかない）
wake ni wa ikanai (ex: sou iu wake ni wa ikanai)

This phrase is often used in the serious situation.
You want to do something, but cannot do (or should not do) it because of being restricted by morals, duty, or responsibility.

I should not do (as you say), or I cannnot do.