All of Carnival Corp.'s North American brands -- Carnival, Princess, Holland America, Cunard and Seabourn -- have modified their paid search requirements and guidelines for third parties, including travel agents, so that others may no longer bid on the lines' branded keywords.

Effective Jan. 1, the lines said that the reason for the new rules is to eliminate confusion online when a consumer does a search for their brand.

"When a consumer searches for Carnival, they're seeking Carnival content and the goal is to provide the cleanest, straight path to the most comprehensive Carnival content available, which is on Carnival.com," said Carnival spokeswoman Jennifer De La Cruz. "This approach of restricting third parties from bidding on a company's branded keywords is becoming commonplace throughout the retail sector."

Princess spokeswoman Julie Benson noted, "We believe most consumers will see this as positive, and will be able to easily find the information they're looking for. They can then take all the info they've researched and bring it to an agency for booking."

The lines' parent company, Carnival Corp., said this is not a corporate initiative but a brand-specific decision.

Carnival Cruise Lines added that it would continue to maintain the travel agency locator on Carnival.com and that travel agencies may continue to include Carnival in the ad text portion of the search results as long as the agency is following Carnival's established guidelines for online advertising.

UPDATE: All of Carnival Corp.'s brands in North America have implemented the new paid search requirements for third parties..