Accord halter

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

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