In the ongoing refugee crisis that’s spread from the Middle East to Europe, maritime shipping has become a lifeline for refugees risking their lives in dangerous sea crossings.

Members of the International Chamber of Shipping (ICS) regularly pick up refugees, many of them fleeing war in Syria and Afghanistan, who have been stranded at sea during attempts to make the journey across the Mediterranean to Europe. ICS estimates that more than 1,000 merchant ships have helped rescue 65,000 refugees since January 2014, according to a recent Reuters report.

Merchant shippers are bound by the United Nations Convention on the Law of the Sea, which includes a humanitarian regulation that requires ships to “render assistance to any person found at sea in danger of being lost,” as long as doing so does not endanger the ship. The cost in lost business for shipping companies can be high—between $10,000 and more than $50,000 per day, depending on the type of ship, Reuters reported.

And there are also concerns about whether the tankers could be getting more than they bargained for.

“We do not know who we are taking onboard: There are no papers, there are no background checks,” Campbell Shipping’s Rajesh Dhadwal, the company’s senior manager for marine and safety, told the news service. “What if, among the people rescued, a few are part of Islamic State or a terrorist organization, and they … take over a tanker?”

The UN rules clearly didn’t anticipate the rescue of tens of thousands of people in a single year, says ICS, which is asking for help from nearby European Union countries.

“The response to the crisis by the Italian Navy and Coast Guard continues to be incredibly impressive,” Peter Hinchliffe, secretary general of ICS, noted in a news release earlier this year. “But the situation is now so serious that all EU member states need to become more engaged.”

ICS has released an array of documents in multiple languages that offer shipping companies guidelines for handling refugees seeking assistance.

“The need to rescue large numbers of people can make the operation particularly challenging,” one such report explains [PDF]. “Experience has shown that effective procedures, supported by drills, will prepare masters and crews to respond safely and to manage successfully rescue operations at sea.”

While ICS has prepared its members to assist refugees, Hinchliffe emphasized that they can’t do it alone.

“Merchant shipping accepts that it has a role to play in this crisis,” he told Reuters. “But we also need support.”

A refugee on board a fishing boat reacts after being rescued in the Mediterranean by the commercial ship CS Caprice. (Handout photo/Reuters)