What action is illegal when it comes to checks according to the insufficient funds law?

Writing a check with knowledge of insufficient funds is illegal because it constitutes an intentional act of deception. This action reflects an understanding that there are not enough funds in the account to cover the amount of the check, yet the issuer still chooses to write the check. This undermines trust in financial transactions and can lead to serious legal consequences, including charges of fraud.

In contrast, holding onto a check for future use is not illegal, as checks can generally be postdated or written with the intention of being cashed later. Writing a check for services performed is also not illegal, provided that there are sufficient funds available when the check is cashed. Cashiering checks typically refers to the process a bank uses to process checks and is not illegal in itself. Therefore, the correct response highlights the specific illegal act of knowingly writing a check without sufficient funds, emphasizing the critical importance of maintaining accountability in financial practices.