A general strike in Greece today (Thursday) could see airports shut and ferry services affected.
In updated travel advice, the Foreign Office warned of protests across the country.
The 24-hour action is in protest against a new labour bill being proposed in the country.
Public sector staff including transport workers, air traffic controllers, health professionals and teachers are to take part in the nationwide industrial action.
The Foreign, Commonwealth & Development Office said: “Ferries may be affected and many airports may closed.
“Check with your transport provider if you are planning to travel by sea or air on 21 September. Buses and Metro services may also be affected.
“Hospital staff are supporting the strike, but emergency services will operate. Consult your hospital directly should you have an appointment planned on 21 September.
“Protests are scheduled across the country with two major rallies scheduled in Athens.”