The deployment of two ships by Royal Caribbean International is being replaced by two other ships.
The Brilliance of the Seas, built in 2002 and scheduled to sail in Europe, will be replaced by the Enchantment of the Seas.
Royal Caribbean didn't reply to a question about why the regulations require swaps.
Next spring and summer, the Brilliance, a 2,543-passenger ship, will travel to Alaska. The ship will leave for Australia in October.
The Enchantment will replace Brilliance in Europe in the spring of 2020. From April to November, the Vision-class ship will sail in the Mediterranean and then on to the Caribbean and the Bahamas.
The passengers will be moved to the substitute ship with the same date. Passengers can rebook on other sailings or get a full refunds.