bone of contention

bone of contention
    n 1: the subject of a dispute; "the real bone of contention, as
         you know, is money"
    

35 Moby Thesaurus words for "bone of contention":
      apple of discord, bone to pick, casus belli, catechism,
      cross-interrogatory, cross-question, crow to pick, crow to pluck,
      debating point, demand, feeler, grounds for war, inquiry,
      interrogation, interrogative, interrogatory, issue, leader,
      leading question, moot point, point at issue, point in question,
      problem, query, question, question at issue, question mark,
      quodlibet, rub, sore point, tender spot, ticklish issue, topic,
      trial balloon, vexed question