Bloggers "crossed the line" when they posted a software key that could break the encryption on some HD-DVDs, the AACS copy protection body has said.
Thousands of websites published the key, which had been uncovered in a bid to circumvent digital rights management (DRM) technology on HD-DVD discs.
Many said they had done this as an exercise in free speech.
An AACS executive said it was looking at "legal and technical tools" to confront those who published the key.
A row erupted on the internet after popular website Digg began taking down pages that its members had highlighted were carrying the key.
The website said it was responding to legal "cease and desist" notices from the Advanced Access Content System.
Digg's users responded by posting ever greater numbers of websites with the key, and the site eventually sided with its users.
Michael Ayers, chair of the AACS business group, said it had received "good cooperation from most folk" in preventing the leak of the key.
He described the row between Digg and its users as an "interesting new twist".
"It started out as a circumvention effort six to eight weeks ago but we now see the key on YouTube and on T-Shirts.
"Some people clearly think it's a First Amendment issue. There is no intent from us to interfere with people's right to discuss copy protection. We respect free speech.
"They can discuss the pros and cons. We know some people are critical of the technology.
"But a line is crossed when we start seeing keys being distributed and tools for circumvention. You step outside of the realm of protected free speech then."
He said tracking down everyone who had published the keys was a "resource intensive exercise". A search on Google shows almost 700,000 pages have published the key.
Mr Ayers said that while he could not reveal the specific steps the group would be taking, it would be using both "legal and technical" steps to prevent the circumvention of copy protection.
"We will take whatever action is appropriate," he said. "We hope the public respects our position and complies with applicable laws."
He added that the copy protection on the HD-DVDs was "absolutely not broken".
The leak of the key meant that some HD-DVD titles could have their copy protection removed and then could be watched on two different software players. The leak of the key did not affect hardware players, he said.
But he accepted that DVDs that had had their copy protection removed were "now in the clear" and could be copied.
He said AACS brought stronger tools to the table than previous copy protection system and said the system had been designed to cope with breaches.