Non-citizen males between 18 and 25 years of age in the United States, who are permanent residents, seasonal agricultural workers not holding an H-2A Visa, refugees, parolees, asylees, and illegal immigrants, are required to register with the Selective Service System.

If you unlawfully failed to register with the Selective Service system, then you would be excluded from employment with the federal government (and be subject to other penalties and exclusions).