An Infantry unit firing out of a hex with a wire obstacle reduces its attack dice by 1. This affects both sides.
Base Rulebook P16
◆ Movement: A unit that enters a hex with Wire must stop and may move no further on that turn.
◆ Battle: An Infantry unit that is on a hex with Wire, will reduce the number of Battle dice it rolls by 1. An Infantry unit that is eligible to battle may remove the Wire instead of battling. Armor must remove the Wire and may still battle.
◆ Line of Sight: Wire does not block line of sight.