Three more major cruise lines on Monday announced plans to require passengers on at least some cruises to show proof of a COVID-19 vaccine.Miami-based Norwegian Cruise Line and its two sister brands, Oceania Cruises and Regent Seven Seas Cruises, said all passengers on departures out of U.S. ports would need to show proof of a COVID-19 vaccine to sail when the brands resume operations later this year.Unlike some lines, the three brands did not announce an exception for younger travelers.For more cruise news, reviews and tips, sign up for TPG’s new cruise newsletter.The announcement came as the brands petitioned the U.S. Centers for Disease Control and Prevention (CDC) to allow them to restart operations from U.S. ports in July.“We believe, that in light of the current health trends, buttressed by the more than 650 million vaccines administered worldwide to date, it is time for [us] to join the rest of the travel, tourism and hospitality sectors in participating in this next phase of our recovery,” Norwegian Cruise Line Holdings president and CEO Frank Del Rio wrote Monday in a letter to CDC director Rochelle Walensky.Norwegian Cruise Line Holdings is the parent company of Norwegian Cruise Line, Oceania Cruises and Regent Seven Seas Cruises.In the letter to Walensky, Del Rio outlined a multipronged plan to resume cruises out of U.S. ports in July that has, at its core, the requirement of a COVID-19 vaccination for all passengers and crew, too.Norwegian Cruise Line operates some of the newest ships in the cruise business, including the 4,004-passenger Norwegian Encore. (Photo courtesy of Norwegian Cruise Line)“Because our return to service plan mandates that the entire population onboard our vessels be vaccinated, our plan reduces the risk of outbreaks and severe COVID-19 cases,” Del Rio wrote.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.The plan also calls for ships sailing from U.S. ports to initially operate at just 60% of capacity, with the capacity total rising by 20% every 30 days.In addition, Del Rio noted the company had spent millions of dollars to add enhanced, hospital-grade air filtration systems to its ships and had significantly upgraded ICU and quarantine medical facilities on ships. The company also has added new contact tracing technology, Del Rio wrote.“Our vessels are well equipped to handle the one-off case of infection that could occur, and our procedures are well detailed and resourced to treat, address and otherwise handle any isolated case on board,” Del Rio said.The CDC has been blocking cruise lines from sailing from U.S. ports for the past 13 months, citing the risk of a coronavirus outbreak at sea. On Friday, the agency released new recommendations for cruise lines that want to restart operations in U.S. waters that suggested the agency was still a long way from allowing cruise ships to restart operations in U.S. waters.In Monday’s letter, Del Rio said he wanted his company’s three brands to resume cruising out of U.S. ports on or around July 4.None of the three Norwegian Cruise Line Holdings brands has operated a single departure anywhere in the world since March 2020. The company is burning through more than $100 million a month as its ships sit idle.In recent weeks, more than a dozen cruise lines have announced plans to require passengers to show proof of a COVID-19 vaccine before sailing. At the same time, a few lines have said they would not require passengers to be vaccinated for COVID-19 — at least for now.Cruise lines that have announced a COVID-19 vaccine requirement for all or at least some upcoming cruises include American Cruise Lines, Celebrity Cruises, Crystal Cruises, Cunard Line, Princess Cruises, Royal Caribbean, Virgin Voyages and Windstar Cruises.Lines that are restarting operations without requiring passengers to show proof of a COVID-19 vaccine include MSC Cruises, and German lines TUI Cruises and Hapag-Lloyd Cruises.Planning a cruise? Start with these stories:The 5 most desirable cabin locations on any cruise shipThe 8 worst cabin locations on any cruise shipA quick guide to the most popular cruise lines21 tips and tricks that will make your cruise go smoothly15 ways cruisers waste money12 best cruises for people who never want to grow upWhat to pack for your first cruise