LONDON (AP) — Thousands of doctors walked off the job in Britain on Wednesday, the start of a six-day strike that was set to be the longest in the history of the state-funded National Health Service.

Managers said tens of thousands scheduled appointments and operations will be canceled during the walkout across England and Wales by junior doctors, those in the first years of their careers. The doctors, who form the backbone of hospital and clinic care, plan to stay off the job until 7 a.m. on Tuesday.

Senior doctors and other medics have had to be drafted in to cover for emergency services, critical care and maternity services.

Julian Hartley, chief executive of heath care managers’ organization NHS Providers, said the strike came at one of the toughest times of the year for the health service, “immediately after the Christmas and New Year period because of the pressures the demands, and of course we’ve got flu, we’ve got COVID.

“So there’s going to be an impact on patients that will be significant,” he said.

Britain has endured a year of rolling strikes across the health sector as staff sought pay rises to offset the soaring cost of living.

The walkouts have strained the already stretched health service still struggling to recover from backlogs created by the coronavirus pandemic.

Nurses, ambulance crews and senior doctors have reached pay deals with the government, but the union representing junior doctors has held out, and negotiations have stalled. The government says it won’t hold further talks unless doctors call off the strike, while the union says it won’t negotiate unless it receives a “credible” pay offer.

“The notion that we’re hellbent on calling strikes and all we want to do is call strikes is not what we want,” said Dr. Vivek Trivedi, co-chair of the British Medical Association’s Junior Doctors Committee. “What we want is to negotiate an offer we can put to our members and for our members to accept it.”