SAN FRANCISCO — The agency governing Internet addresses on Friday approved the creation of a new red-light district on the Web, but the decision may not end years of fighting over the contentious plan.

The Internet Corporation for Assigned Names and Numbers authorized the creation of an .xxx suffix for pornography Web sites. The decision was immediately slammed by some of the sex industry’s biggest names.

Industry members say they fear they could be subject to arbitrary censorship by governments and even by a new board overseeing the dot-xxx domain. They also say the plan would unfairly force existing pornography sites to register their sister domain names ending in xxx to prevent other businesses from using the names.

“Our industry is unanimously opposed,” said Diane Duke, executive director of the Free Speech Coalition, a trade association representing more than 1,000 pornography businesses. Ms. Duke said that she expected the association’s members, which include companies like Hustler and Adam & Eve, to continue to use dot-com addresses. She also said the association was considering its legal options.