The Trump administration on Tuesday imposed new restrictions on Americans going to Cuba, banning the most common way Americans travel to the island.

Beginning on Wednesday, the United States will not permit group educational and cultural trips known as “people to people” trips to the island unless they were booked before June 5, the Treasury Department said in a statement. Nor will it allow cruises, private yachts or fishing vessels to stop in Cuba. Group people-to-people trips have been used by thousands of American visitors.

The move left tour companies and cruise lines assessing the impact and how they might have to modify their operations in Cuba.

C​ruises have become the most popular way for Americans to travel to Cuba since 2016, when President Obama reopened relations with the island. ​This year, between Jan. 1 and April 30, 142,721 Americans went to Cuba on​ cruises, ​compared to the 114,832 who ​traveled there by plane. Th​ese numbers do not​ ​include Cuban-born Americans visiting family​.