D.C. Code § 16-513
It is unlawful for an employer to pay salary or earnings to an employee in advance of the time they are due and payable, for the purpose of avoiding or preventing an attachment or garnishment against the earnings or salary of the employee, and such an advance payment, as to the attaching creditor, is void.
After the service of one writ of attachment or garnishment on a judgment against an employer, any payment of salary or earnings thereafter before the time when the salary or earnings are due and payable made within a period of six months after the date of service of the writ or before the earlier satisfaction of the judgment, whichever is the earlier, is as to such attaching creditor presumed to be in violation of this section and casts upon the employer the burden of proving that the advance payment or payments were not for the purpose of avoiding the attachment of the salary or earnings.
D.C. Code § 16-513