Our management advised that all future new hire pilots will be U.S. citizens; and that all of our non citizen pilots ("Green Card" holders) have 12 months to become citizens or be fired. Not a threat, just a statement of fact. Assuredly, sooner or later this policy may generate legal activity. Constitutionally it may be a flawed policy, but until it's tested in the courts it's reality. What has generated this security overload is AMC. The Air Mobility Command (USAF) has required all contractor aircraft to be operated only by U.S. citizens.