Former adviser to President Trump Steve Bannon knows a thing or two about the president. And he believes Apple might be fighting the wrong fight over iPhone unlocking.

Speaking in an interview on CNBC's Squawk Box on Wednesday, Bannon (who no longer works for the president) said that Apple should heed Trump's warnings on iPhone unlocking and consider it tantamount to a papal bull, a term used to describe directives the pope issues when he wants to make a decree.

"If I were the guys at Apple, I would pay attention to President Trump's tweets," Bannon said. He added that there's a very real possibility that the president will "drop the hammer" on Apple and other big tech companies that want to preserve encryption in the face of law enforcement investigations.

Bannon's comments come amid a growing controversy between Apple and the Trump administration over whether the company should bow to the government's pressure and unlock password-protected iPhones used by Saudi Air Force 2nd Lt. Mohammed Saeed Alshamrani, who shot three people at the Pensacola Naval Air Station in December. Alshamrani was killed at the station, and the U.S. has called it an act of terrorism.

This week, the Trump administration has ramped up its criticism of Apple for not building a backdoor into the iPhones to make it easy for law enforcement to access Alshamrani's data. Attorney General William Barr said Apple hasn't provided "substantive assistance" to unlock iPhones.

For its part, Apple has said that it won't provide a backdoor, holding up a longstanding policy at the company to not provide a method by which its iPhone encryption can be circumvented by anyone, including law enforcement. 

Trump has upped his criticism of Apple in recent days, and said on Tuesday that the company should help law enforcement immediately.

"We are helping Apple all of the time on TRADE and so many other issues, and yet they refuse to unlock phones used by killers, drug dealers and other violent criminal elements," Trump tweeted. "They will have to step up to the plate and help our great Country, NOW! MAKE AMERICA GREAT AGAIN."

Apple has responded to the criticism by saying that it has providing round-the-clock help to law enforcement on the matter. The company hasn't built a backdoor into the iPhone, but Apple says that it handed over large amounts of data to aid investigators. Apple has also said that it will continue to work with investigators.

Still, Bannon's point is well taken. The president is not known to take kindly to companies or individuals challenging him or not doing what he wants. Amazon has even cried foul after it lost a major, $10 billion JEDI contract for government cloud computing to Google. Amazon contends that the president's dislike of CEO Jeff Bezos may have played a role in the decision.

So far, Trump and Apple CEO Tim Cook have had a cozy relationship that has benefited the company on trade and other matters. Whether that will change over this latest spat remains to be seen.