If you're arriving in Athens Greece in the next couple of days, your transportation options may be more limited than usual. Some public transportation in Athens, including the Metro and the electric railway system, will start later than usual on Wednesday, December 19th, with the first operations commencing at 9am, though this will vary depending on the station.
TrainOSE is also suspending operations in the city and across the country on both Wednesday and Thursday. On the bright side, long-distance KTEL buses will be operating as usual.
http://apergia.gr/index.php
This is a link to a greek web site dedicated to strike information. Yes, strikes have become so endemic that one needs a website to be prepared. Google can translate the page well enough.