The main three reasons for the Courts to pierce the corporate veil and impose personal liability on officers, directors, shareholders, or members when

1) There is no real separation between the company and its owners:
For instance, if the owner pays personal bills from the business checking account or ignores the legal
formalities that a corporation or LLC must follow (for example, by making important corporate or LLC
decisions without recording them in minutes of a meeting)

2) The company’s actions were wrongful or fraudulent:
If the owners borrowed money recklessly and lost it or if owners made business deals knowing the business
couldn’t pay the invoices

3)The company’s creditors suffered an unjust cost:
When a third party is left unpaid after doing business with them or when the court observes there
are unfair business practicesses

Source: https://www.nolo.com/legal-encyclopedia/personal-liability-piercing-corporate-veil-33006.html