41 CFR 304-3.12: -3.12 Spouse travel paid by non-Federal source.

A non-Federal source may pay for an employee's spouse to accompany them when it is in the interest of and authorized in advance by the employee's agency. All limitations and requirements of this part apply to the acceptance of payment from a non-Federal source for travel expenses and/or agency reimbursement of travel expenses for the employee's accompanying spouse. The agency may determine that a spouse's presence at an event is in the interest of the agency if the spouse will—

(a) Support the mission of the agency or substantially assist in carrying out the employee's official duties;

(b) Attend a ceremony at which the employee will receive an award or honorary degree; or

(c) Participate in substantive programs related to the agency's programs or operations.