Elaborating on what was mentioned above by both amandaally1029 and thuytienlecao in the above posts, I found the 3 most common occasions a court will rule to pierce the cooperate veil are: No real separation between the company and its owners, the companies actions were deemed fraudulent, or the company’s creditors suffered an unjust cost. Legal separation becomes blurred and an issue when a company owner uses a company credit card to pay off personal expenses or the owner neglects to follow vital LLC rules and guidelines. In addition, if the owner of a company was deemed to reckless borrow (and then lose) money, the courts can rule to pierce the veil to reclaim the borrowed amount though company/ owner assets. Unjust costs to creditors occur when a merchant of an LLC has unpaid bills that coincide with breaking the general guidelines of an LLC.

An interesting trend regarding the prevalence of breaking the corporate veil tends to show that smaller companies are more likely to commingle assets than larger companies. This is because the owner is more likely trying to balance work and home expenses and some have been known to shift assets around (either intentional or unintentionally) to benefit either their business or house mortgage for example. These are grounds for the court to break the veil should trouble arise involving the LLC.

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