Workers at Evangelismos Hospital in central Athens will hold a rally at the emergency unit on Wednesday morning to protest against a decision by its director to forbid public statements by staff without his permission.
In a statement, the union of hospital doctors in Athens and Piraeus (EINAP) denounced what it called "an autocratic" move by the director.
Greek police were called to break up a protest at a migrant hotspot on the island of Chios in the eastern Aegean on Tuesday.
Migrants at the Vial facility were protesting the slow pace with which Greece has been processing asylum claims.
Some protesters lit a garbage container on fire and then threw stones at firemen who tried to douse the blaze.