While there is no law requiring that nonessential employees be compensated if they are ordered off the job, Congress has in the past voted to reimburse their losses once shutdowns ended.
Even if Congress fails to resolve its budget standoff by the deadline Monday and much of the government runs out of money, civilian and military personnel who are considered vital to national security, public safety, health and welfare would be called to work — about 1.3 million civilian employees and 1.4 million in the military.
By law, they all must be paid. But the law does not say when.
Source: Washington Post