Police in Greece's second city Thessaloniki on Saturday fired tear gas at anti-vaccination protesters ahead of a keynote economic speech by Prime Minister Kyriakos Mitsotakis.
The police used tear gas and a water cannon to keep around 1,000 protesters away from the venue of the PM's speech.
There has been opposition in Greece to the mandatory COVID-19 vaccination of all health workers, who are threatened with suspension if they fail to comply.
Tougher air, sea and rail transport restrictions also come into effect on Monday, with the unvaccinated no longer entitled to free testing.
Over 14,000 people in Greece have died from causes related to the pandemic. Over half of the country's 11 million residents have been fully vaccinated.