Greek island ferries were tied up in port on Tuesday and Athens public transport, hospitals and state schools faced disruptions as unions went on strike against proposed labor reforms.
Police said about 8,000 people marched peacefully through central Athens as they took part in three separate demonstrations called by unions and left-wing groups.
The 24-hour strike by the civil servants' umbrella union and other labor groups knocked out most forms of public transport in Athens, although the capital's underground was functioning for most of the day.
Large traffic jams were reported in many parts of Athens.
Seamen's unions went ahead with their strike that affected the ferry system, despite a court ruling it illegal.
Unions oppose parts of proposed legislation that would make it harder to call strikes and would allow workers to vote remotely on industrial action without attending meetings. It also would allow changes in some collective work agreements.