Invoking an 18th century law, the government is attempting to justify accessing our iPhones.

But Apple is refusing to let that crumble the firewall protecting its customers.

Using the All Writs Act — passed in 1789 — the FBI has requested Apple allow it to access the cellphone of San Bernardino, California, shooter Syed Rizwan Farook, asking the company to create a new version of the iPhone operating system to circumvent several security features.

In response, Apple CEO Tim Cook published a letter Tuesday on the company’s website — you probably spotted the now-viral post on your Facebook timeline. The letter warns customers that such an alteration in the operating system could become a breach of consumers’ security. This “overreach by the U.S. government” could extend to intercepting everything from messages and iPhone camera access to health records and financial data.

The action would be an unprecedented and irresponsible use of power by the FBI, effectively putting millions of consumers’ personal information at risk.

The antiquated statute grants federal courts the authority to issue court orders that request third-party assistance, which the government has used in prior cases to request information for individual defendants in criminal cases.

But here, the FBI isn’t simply asking for access to a single iPhone.

A potential new version of the iPhone operating system that would satisfy the government’s needs would be a lofty request it has never sought before. It would provide the FBI the ability to access all iPhone users’ data, undoing decades of security research and advancements. But the two-century old All Writs Act was created when the only form of personal security was a musket.

Cook warns that compliance with the government could entail a “backdoor to the iPhone,” and the ramifications of such a precedent could be tremendous. Not only could the government use this 227-year-old law to collect information on millions of Apple customers, but it could directly interfere with the company’s products — which means the government is overstepping its role.

And Apple has every right to protect itself and its customers.

Stephen Vladeck, a professor at American University Washington College of Law, told The Wall Street Journal, “The real question is where the line is between when the government can get an order to compel a third party to do something and when it cannot.”

When the government asks a technology company such as Apple to alter its products and undermine decades of security advances, it is within the company’s right to decline because it isn’t an agent of the government.

“We believe it would be in the best interest of everyone to step back and consider the implications,” Cook writes.

Stakes are high, but Apple is well equipped with legal defense to assure customers their trust won’t be undermined.

We rely on Apple to protect our data — and for now, we can rest easy knowing they will.