The Tal Law deals ONLY with yeshiva students. It has nothing to do with Israeli Arabs, who are not - and never have been - exempt from callup for military service. Ehud Barak can call Israeli Arabs up tomorrow, and if he did then they MUST report for service. No change in legislation is required: Barak merely needs to change the current administrative policy, which is to not bother to call them up.
U.S. to defend Syrian rebels with airpower, including from Assad (Reuters)
from the article: IDF enlistment for all: An ongoing debate