Getting into legalities might not be the proper way to address the issue. If you want to prohibit incurring debt from a co-worker, you can include this in the company's ethical standards in the Employee Handbook. For example, instead of outright prohibiting debt from co-worker, you can frame it as an ethical standard by stating that all persons are required to pay their lenders, whether co-workers, relatives, or friends.
You may want to teach employees how to lend money. An example would be a Promissory Note where the debtor promises to pay a certain amount every payday to the lender. You can go even further by requiring the debtor to sign a document where debtor allows the company to deduct the payment of debt to another employee through salary deduction. The consent of the debtor to salary deduction is important. Do not omit this step. The proceeds of the payment will be credited to the lender. That way lender is assured of payment. If the debtor does not agree to a salary deduction, then the lender should not lend him any money.
This is just one item in the company's ethical standards. To be able to inform employees, package the ethical standards in such a way that there are other standards that an employee has to comply with. You can discuss the company ethical standards during orientation of new employees or general company meeting. I am suggesting the packaging of ethical standards in order to prevent "kapalmuks" borrowers from thinking that they are the target of the ethical standards.