The United Kingdom’s state-funded health care service is facing what is being touted as its longest-ever strike as thousands of doctors in England commenced a five-day walkout over pay.

Junior doctors, at the early stages of their careers in the years after medical school, began their strike early Thursday, with many of them making their case for a 35% pay rise in picket lines outside hospitals across England.

The U.K. government, which is facing a host of strikes by public workers across many sectors, is standing firm to its belief that it won’t negotiate while the strikes are taking place.