Travel company Expedia has stopped selling holidays that involve performances by dolphins and whales in captivity.
"As a result, attractions and activities that involve performances by or interactions with dolphins and other cetaceans will no longer be available on our sites."
A spokesman told the Mail on Sunday that the company will continue to sell tickets to "seaside sanctuaries that provide captive animals with a permanent seaside living environment" if they "are accredited and do not feature interactions or performances".
The firm said the change will take time to implement and it intends to complete the process by early 2022.
The tourism practice has come under criticism from prominent figures like Carrie Johnson, the prime minister's wife, as well as animal rights activists.
Virgin Holidays made a similar move in 2019, announcing it would no longer sell tickets to these kinds of attractions or experiences.
SeaWorld parks in San Diego and Florida are among those that will be affected, having struggled to combat public perception of its parks since the 2013 documentary Blackfish shined a light on the lives of killer whales in captivity.
Animal rights group PETA praised the decision, saying it comes after its campaigners were encouraged to flood Expedia's president with calls and messages.
"PETA congratulates Expedia for officially rejecting cruel 'swim with dolphins' encounters and SeaWorld prisons," said PETA executive vice president Tracy Reiman.
"PETA urges people to take note and do their part by refusing to support such animal-exploiting operations."
The group alleged that dolphins that swim with tourists are confined to barren tanks or makeshift lagoons with no choice but to swim in endless circles.
"Many die prematurely because of the stressful conditions of captivity, " it claimed.
Wildlife charity World Animal Protection called it "amazing news" that would hopefully prompt change throughout the industry.
The charity's campaign manager for wildlife Katheryn Wise said: "Travel companies play a huge role in driving captive dolphin entertainment and as one of the largest travel companies in the world we are delighted that Expedia Group are making a stand.
"It's time for other travel giants like TUI to do the right thing and follow suit."
SeaWorld has previously said that animal activists manipulate marine science to advance their agendas, adding: "With rising threats to our oceans and their inhabitants, supporting independently accredited zoological facilities is more important than ever.
"No company does more to protect marine mammals and advance cetacean research, rescue and conservation than SeaWorld."