Some of the world's biggest banks are urging a U.S. judge not to immediately terminate LIBOR after a group of borrowers filed suit claiming the benchmark was the work of a "price-fixing cartel."

Defendants in the case, including JPMorgan Chase & Co., Credit Suisse Group AG, and Deutsche Bank AG, said in a November filing that an injunction abruptly ending the London interbank offered rate (LIBOR) would wreak havoc on financial markets and undermine years of work reforming the reference rate. The plaintiffs, which include 27 consumer borrowers and credit-card users, are also seeking monetary damages.

Attorneys not involved in the case say the chances of an injunction are slim. Yet it underscores the risks and legal costs for banks that continue to prop up LIBOR, which still underpins hundreds of trillions of dollars of financial assets around the world. It also highlights the fragility of the discredited benchmark—which, in theory, could be halted by a single court decision.