Holland America and Princess Cruises canceled several sailings that were scheduled to take place at the start of Alaska’s 2021 tourist season.

The cancellations are a sign that the continuing coronavirus pandemic could have a major impact on Alaska’s 2021 tourist season, just as it did on last year’s.

Princess and Holland America — both subsidiaries of Carnival Corp. — said in statements Wednesday that rules imposed by the Centers for Disease Control and Prevention, “in addition to the uncertainty around travel restrictions,” prompted the companies to cancel trips through at least mid-May.

Princess canceled six Alaska trips scheduled through May 15. Holland America canceled sailings on three Alaska-bound ships through the first week of June and on three others through mid-May. Carnival Cruise Line canceled all sailings through March 31 but has not yet canceled any Alaska voyages.

Celebrity Cruise Lines and Norwegian Cruise Lines, two competing companies that also offer large-ship cruises to Alaska, have not yet canceled Alaska-bound voyages, but are expected to announce similar actions.

Large cruise ships are under severe restrictions when sailing to or from American ports under an order from the CDC, and most cannot sail at all.

Large ships bound for Alaska also must contend with Canadian restrictions because all are registered outside the United States, and federal law requires foreign-flagged ships sailing between two U.S. ports to stop at a foreign port in between.

For Alaska cruises, a stop in Canada satisfies that requirement. But Transport Canada, the Canadian regulator, has banned all cruise ship traffic through March, and a decision is expected soon on whether or not to extend that ban.