Poland's state-funded health care is chronically strapped, understaffed and poorly organised.
In some regions, the wait for free procedures can take years. Low earnings can force doctors to work overtime, though wage increases took effect Monday.
The Health Ministry said today that some 3,500 doctors have opted out of contracts that allowed for work weeks of more than 48 hours. The protesters say the number is more like 5,000.
The opposition is calling for the health minister's dismissal in an expected government reshuffle.