“We must not allow this dangerous precedent to be set,” Mr. Koum wrote. “Today our freedom and our liberty is at stake.”

But behind the scenes, there was discomfort among some companies that have generally allied themselves with Apple on the topic of government surveillance.

All of the companies involved in Reform Government Surveillance, including Apple, acknowledge that they often comply with law enforcement requests for customer data when under order from a court. Apple’s stance in this case seemed overly antagonistic to some companies in the coalition, according to people privy to conversations on the matter who spoke on condition of anonymity because they were not authorized to speak on the record.

In its statement on Wednesday, Reform Government Surveillance chose its words carefully. The association’s member companies, the statement said, “remain committed to providing law enforcement with the help it needs while protecting the security of their customers and their customers’ information.”

There was also disagreement about Apple’s tactics. Gunter Ollmann, chief security officer at Vectra Networks, an information security company in San Jose, Calif., argued that the government’s demand that Apple help unlock the San Bernardino shooter’s iPhone was in line with similar one-time requests and that Apple was creating an unnecessarily high-stakes battle by framing the unlocking as creating a universal back door.

“I’m concerned that since Apple has attempted to deny the F.B.I. request citing use of ‘back doors,’ should they lose this legal argument, the repercussions could be extensive to the entire security industry,” he said in a blog post.