ATHENS, Greece (AP) — Greek island ferries are tied up in port for a second day because of a strike by crews, whose main union is debating whether to extend the walkout for another day in pursuit of salary increases.

The strike, set to end Wednesday morning, has left tens of thousands of travelers and islanders stranded, since most islands have no air link with the mainland.

The PNO union will debate prolonging the strike later Tuesday. PNO is pressing for a 5-percent pay increase after an eight-year freeze because of Greece's debt crisis.

Ferry operators have offered a 2-percent pay hike over the next 15 months. Their association has warned that the strike would have an adverse effect on tourism — a key source of revenue for Greece's economy.