Citing growing concerns of global terrorism and the possibility of violence in certain port cities, several cruise lines are curtailing their calls to Turkish port cities.

The most recent is Norwegian Cruise Line Holdings Ltd., which announced at the end of January it would stop making calls at Turkey altogether following a recent attack in Istanbul.

“At Norwegian Cruise Line, Oceania Cruises and Regent Seven Seas Cruises, our primary concern is to ensure the safety and security of our guests and crew. Due to recent events in Turkey, we are suspending all calls to the country through 2016 across all NCLH brands. We will continue to closely monitor the situation and make future itinerary adjustments as appropriate. We have begun the process of informing guests booked on the affected cruises of the itinerary changes and will update the respective brand websites with revised voyage information,” the company said in a statement.

In the past few months, companies like Oceania Cruises and Regent Seven Seas Cruises join Celebrity Cruises, Crystal Cruises, Holland America Line, MSC Cruises, Royal Caribbean International and Seabourn Line in similarly altering their itineraries to Turkey.