The President of the United States designates a combat zone by Executive Order as an area in which the U.S. Armed Forces are engaging or have engaged in combat. Publication 3 lists the specific areas and dates.
Hazardous duty areas are determined by Congress. Members of the Armed Forces deployed overseas, away from their permanent duty station, in support of operations in a qualified hazardous duty area, or performing qualifying service outside the qualified hazardous duty area, are treated as if they are in a combat zone for income tax purposes.
A taxpayer serving in a combat zone may qualify for relief from certain IRS compliance actions, such as audits or enforced collections, until 180 days after the taxpayer has left the zone.
Taxpayers qualifying for such combat zone relief may notify the IRS directly of their status through a special e-mail address: email@example.com. They should provide name, stateside address, date of birth and date of deployment to the combat zone. They should not include any social security numbers in an e-mail. This notification may be made by the taxpayer, spouse, or authorized agent or representative. For more information visit www.irs.gov.
An area's combat zone status usually changes on the dates the President designates by Executive Order.