Issue that halts negotiations

• Accord halter
• Negotiations killer ... or, in a way, what each answer to a starred clue is
• Negotiations killer
• Fatal relationship problem
• Negotiation obstacle
• Negotiator's outrageous demand, e.g.
• Non-negotiable issue
• Negotiator's outrageous demand, e.g

Wiktionary Word definitions in Wiktionary
n. (alternative spelling of deal breaker English)