20 C.F.R. § 655.153
The employer must contact, by mail or other effective means, U.S. workers employed by the employer in the occupation at the place of employment during the previous year and solicit their return to the job. This contact must occur during the period of time that the job order is being circulated by the SWA(s) for interstate clearance under § 655.150 and before the date specified in § 655.158 . Documentation sufficient to prove contact must be maintained in the event of an audit or investigation. An employer has no obligation to contact U.S. workers it terminated for cause or who abandoned employment at any time during the previous year if the employer provided timely notice to the NPC of the termination or abandonment in the manner described in § 655.122(n) .
20 C.F.R. §655.153