LONDON (AP) — Medical appointments and minor operations were canceled across Britain on Thursday, as thousands of doctors took part in their first industrial action in almost 40 years to protest changes to their pensions.

The British Medical Association, a doctors’ union, said the 24-hour action was not a strike — doctors showed up for work, but were refusing to do non-urgent procedures or paperwork.

It was the first time in 37 years that British doctors had staged an industrial action, though health officials said the overall impact on services was limited.

Though the medical association represents 100,000 doctors, Britain’s health ministry said that only about 11,500 had joined the action. About onequarter of doctors’ practices were affected, with about 2,000 health centers reporting that at least one staff member had joined the protest.

Around 2,700 non-urgent operations were canceled and 18,750 outpatient appointments had to be rescheduled as a result of the action, the ministry said.