Junior doctors are set to walk out on strike in Sheffield this week.
The British Medical Association has called three-walkouts - the first next Tuesday - after talks over a contract dispute broke down.
The union had until midnight on Monday to decide whether it wanted to take industrial action or face having to re-ballot its members.
The strike will run from 8am on Tuesday to 8am on Wednesday, and from 8am on January 26 to 8am on January 28.
Emergency care will be covered on the first two strikes. But a further spell of industrial action, from 8am to 5pm on February 10, is planned to be a full walk-out.
The government says change is needed to create more seven-day services.
Health chiefs in Sheffield have said contingency measures are in place.