red line

plural red lines

1. hobbiesThe thick red line on the ice which divides the rink in half.
2. figurativelyA boundary or limit which should not be crossed.

   The administration’s ultimatum now seems like cheap talk, and it illustrates the risks of carelessly drawing red lines and issuing highly public threats that won’t be enforced.

   2013 May 4, Daniel Byman, “Mr. Obama, Don’t Draw That Line”, in The New York Times, →ISSN

   3 more examples

   After a failed attempt by ministers to bounce the union into an agreement by announcing its terms (which included all sorts of union red lines such as drivers having to pay for their own training) in the media rather than over the negotiation table, there is an understandable reluctance on the part of the unions to engage in any discussions unless there are no preconditions.

   2023 September 6, Christian Wolmar, “Rail strikes: little prospect of negotiations”, in RAIL, number 991, page 44

   “Now that the red line of overt and direct strikes on Iran’s soil has turned pink, Israel is playing to its own strength and exploiting Iran’s conventional weakness,” [Ali Vaez] adds.

   2024 October 28, Scott Peterson, “Israeli strikes inside Iran cross a threshold. How will Iran respond?”, in The Christian Science Monitor

   “We’ve made very clear what our red lines are,” Mr. Vance told reporters, “what things we’re willing to accommodate them on.” He added, “They have chosen not to accept our terms.”

   2026 April 12, Tyler Pager, David E. Sanger, “What Now? Vance Leaves Iran Talks Without a Deal.”, in The New York Times, →ISSN

3. Used other than figuratively or idiomatically: see red, line.