Apple CEO Tim Cook. AP The Department of Justice has said that Apple must comply with the FBI's request to create software enabling law enforcement to access data on an iPhone used by one of the San Bernardino shooters.

In a motion filed on Friday, the department is asking the judge in the case to immediately order Apple to cooperate with the FBI investigation.

The motion said Apple's refusal to unlock the iPhone "appears to be based on its concern for its business model and public brand marketing strategy."

"Rather than assist the effort to fully investigate a deadly terrorist attack by obeying this court's [order], Apple has responded by publicly repudiating that order," prosecutors wrote in the filing.

The DoJ motion argues that Apple's technical ability is critical to unlock the iPhone used by Syed Rizwan Farook, one of the attackers in the San Bernardino rampage last December.

Earlier this week, CEO Tim Cook posted an open letter on Apple's website explaining why Apple would resist a judge's order for the company to help the FBI access data on a single iPhone.

Cook wrote:

We have great respect for the professionals at the FBI, and we believe their intentions are good. Up to this point, we have done everything that is both within our power and within the law to help them. But now the U.S. government has asked us for something we simply do not have, and something we consider too dangerous to create. They have asked us to build a backdoor to the iPhone.

The Senate Intelligence Committee decided on Thursday against proposed legislation that would impose criminal penalties on companies that have declined to comply with court orders, according to The Wall Street Journal.

Apple's legal response is expected before February 26. The DoJ is expected to release a formal statement later today. A federal court hearing in California has been scheduled for March 22, according to Reuters.