〜（よ）うものなら

Meaning

Expresses an extreme hypothesis, "if one were to do such a thing, it would be disastrous." Used with caution or exaggeration that even doing so slightly invites grave consequences.

Examples

締め切りに一日でも遅れようものなら、契約は打ち切られる。 If you are even one day late with the deadline, the contract will be terminated.