Action comes out of conscious decision. Reaction comes out of impulsiveness. Impulsiveness creates a chain of karma.
Reaction and non-action both create karma, but conscious action transcends karma. Although conscious action does not create new karma, non-action can. A soldier shooting in war and a policeman using tear gas do not create karma, but a doctor who fails to give medicine to a patient in need incurs karma.
Through knowledge and devotion, transcend all karma and be free.