Up to 20,000 doctors in Germany have said they are escalating industrial action by going on indefinite strike.
It is the biggest health sector strike in Germany's post-war history
The dispute is over pay and working conditions at state-run hospitals as well as at 40 university clinics.
Some of the hospitals are in cities staging the World Cup, including Cologne, Munich and Leipzig.
Thousands of doctors have already stopped work, delaying some operations. The doctors began their industrial action three months ago.
Their union says they work on average 60 to 80 hours a week - double the number in their contract.
The doctors are also demanding a 30% pay rise.
Many German doctors have moved abroad to work, the BBC's Tristana Moore reports from Berlin. In the UK, for example, they can earn about twice as much and work fewer hours.
The doctors' union held talks with the employers' association on Saturday.
Union leaders are meeting in Frankfurt later on Monday to discuss a new offer that is on the table.