Generally, to remain qualified, plans must prevent distributions to employees before death, retirement, termination of service, or retirement.
Borrowing money from a retirement plan is a Prohibited Transaction. The Department of Labor recognized that participant loans are a legitimate investment vehicle, and granted a Prohibited Transaction Exemption for loans to plan participants.
To stem perceived abuses, IRS and DOL have issued rules and regulations which must be followed to prevent participant loans from being considered distributions (taxable income) to borrowers.