U.K. regulators warned financial firms they are intensifying their scrutiny of Libor transition plans and that managers who fall short should get smaller bonuses.

The Bank of England and the Financial Conduct Authority said in a letter to chief executives that they have tools they can use on firms making insufficient progress before an end-of-year deadline.

Senior managers responsible for the task “should satisfy themselves that all appropriate actions are being taken,” the BOE and the FCA said in the letter. “As a key regulatory priority, we expect that this transition forms part of the performance criteria for determining their variable remuneration.”

Libor, linked to everything from mortgages to derivatives, has long been discredited by manipulation scandals, yet it still underpins hundreds of trillions of dollars of assets around the world.

The BOE’s latest effort to push banks to be ready for its retirement comes ahead of a key U.K. milestone next week. From Thursday, firms have been told to stop issuing linear derivatives, loans, bonds and securitizations linked to sterling Libor.

Regulators may view continued use as poor risk management, and singled out the syndicated lending business for particular pressure. A number of firms within the business may be undermining the switchover and should not be allowed to put a brake on the transition, the BOE said in Friday’s letter.

“Any new sterling Libor syndicated lending commitment after the end-Q1 milestone would be viewed as a collective failing of all the banks in the syndicate,” they said.

In a separate development on Friday, regulators raised the prospect that an artificial sterling Libor number could be published for up to a decade after the controversial benchmark is scrapped.

Concerned that some troublesome financial contracts won’t be able to switch to replacement benchmarks, the FCA plans to publish a “synthetic” London interbank offered rate. The BOE said that the FCA’s power to do this will need to be reviewed annually for a maximum of 10 years.

Most Libors are due to expire at the end of 2021, but regulators are concerned that bonds and securitizations risk descending into a legal limbo because they lack provisions necessary to switch and are too complicated to renegotiate.

The U.S. is planning to avoid synthetic Libor and instead New York state lawmakers approved legislation this week to smooth the transition, with the Federal Reserve calling for similar legislation at a national level. The BOE said the approach for dollar Libor tenors ending in mid-2023 would be kept under review.