Federal regulators are prepared to take action against sellers of Internet access that want to restrict what their customers can do online.

Kevin J. Martin, chairman of the Federal Communications Commission, said Friday that Comcast, the nation’s largest cable company, should be sanctioned because it had interfered with the Internet connections of users who were exchanging files with other people.

Mr. Martin’s recommendation is a strong push for network neutrality, the idea that Internet access providers like Comcast should not be allowed to favor some uses of their networks over others. Internet companies like Google and free speech advocates have backed this approach.

The cable and phone companies that provide most of the nation’s Internet service have argued that such rules were not needed. They have said that they should be free to run their networks as they see fit, and that there had been no cases of problems with such discrimination.