WASHINGTON—A majority of members of the Federal Communications Commission have cast votes in favor of punishing Comcast Corp. for blocking subscribers’ Internet traffic, an agency official said Friday.

Comcast, the nation’s largest cable company, was accused of violating agency principles that guarantee customers open access to the Internet.

Three commissioners have voted in favor of an order reaching agreement with the finding, enough for a majority on the five-member commission. But the decision will not be final until all five members have cast their votes. The commission is scheduled to take up the issue at its Aug. 1 meeting.

The three votes in favor were Democrats Michael Copps and Jonathan Adelstein and Republican chairman Kevin Martin, who recommended the company be found in violation, according to the official, who asked not to be named because the vote was not yet final.

The potentially precedent-setting move stems from a complaint against Comcast Corp. that the company had blocked Internet traffic among users of a certain type of “file sharing” software that allows them to exchange large amounts of data.

The text of the order is not public. But Martin has said it will not include a fine. He also said it will require Comcast to stop its practice of blocking; provide details to the commission on the extent and manner in which the practice has been used; and to disclose to consumers details on future plans for managing its network going forward.

The FCC approved a policy statement in September 2005 that outlined a set of principles meant to ensure that broadband networks are “widely deployed, open, affordable and accessible to all consumers.”

The principles, however, are “subject to reasonable network management.”

Comcast spokeswoman Sena Fitzmaurice in a statement released Friday night said the company’s network management practices are “reasonable, wholly consistent with industry practices and that we did not block access to Web sites or online applications, including peer-to-peer services.”

The action is the first test of the agency’s network neutrality principles. Members of both the House and Senate have sponsored network neutrality bills, but they have never come close to becoming law.

Large Internet service providers have fought against such regulation, arguing that it is a solution in search of a problem and that companies that spend billions on their networks must be free to manage traffic.