PNO is calling on all passengers and workers to show understanding and support, "as this fight is not just sailors' business, but the affair of the whole Greek society," according to a statement on its website.
Fourteen seafarers' unions have decided to participate in a general strike planned for February 4 to escalate the protests against the pension reforms.
Previous Greek seamen strikes took place on January 20 and 21. In early November, ferry services connecting the islands were suspended for four days.
Protests against pension reforms and tax hikes are underway across Greece. Farmers have been blocking roads for several hours every day. Rallies are regularly held in Athens, bringing workers, lawyers, doctors, engineers and scientists into the streets.