Windstar has confirmed it will require all guests to provide proof of Covid-19 vaccination to sail with the firm "until further notice".
The line said the move was in the best health and wellness interests of guests, crew and those living in the places where the yacht specialist plans to call.
"Many Windstar destinations and some airlines have announced, or are considering, vaccine mandates, providing further support for the new Windstar policy," said the line in a statement.
President Christopher Prelog said vaccination was "another layer of safety" for all, stressing the line’s insistence on vaccination was the "responsible course of action".
"Looking at the science behind the virus, we see consistent recommendations for wearing masks, social distancing, testing, and enhanced cleaning," said Andrew Todd, chief executive of Windstar and parent Xanterra Travel.
Todd added the line’s Beyond Ordinary Care programme ensured "hospital-grade" measures across air filtration, germicidal irradiation and surface sanitisation.