The US International Trade Commission, the federal agency that handles trade-related mandates, previously issued an order that would prohibit Apple from importing the Series 9 and Ultra 2. The decision came after a US judge ruled in January that Apple infringed on Masimo patents related to the technology used in Apple's blood oxygen sensing system. The order is currently under presidential review, but Apple is preemptively pausing sales in case the decision is upheld, the company said. The move was first reported by 9to5Mac on Monday, and Apple has since confirmed its decision to CNET. 

The Apple Watch is one of Apple's most important products, helping push the company's wearables, home and accessories business to be its second-largest product category behind the iPhone. Apple has previously said the size of its wearables unit alone equals that of a Fortune 150 company. 

Apple will stop selling the Series 9 and Ultra 2 through its website on Dec. 21, while Apple stores will stop selling the watches on Dec. 24.

"Apple's teams work tirelessly to create products and services that empower users with industry-leading health, wellness and safety features," the company said in a statement to CNET. "Apple strongly disagrees with the order and is pursuing a range of legal and technical options to ensure that [the] Apple Watch is available to customers."

The company added that it will "continue to take all measures to return [the] Apple Watch Series 9 and Apple Watch Ultra 2 to customers in the US as soon as possible," if the order stands.

Apple's pause of Apple Watch sales comes during the critical holiday shopping season. Smartwatches were among the top products sold during the Black Friday period, according to holiday shopping data from Adobe. 

When the judge's ruling was made in January, Masimo CEO Joe Kiani said the decision "should help restore fairness in the market."

Here's what to know about Apple's pause in sales of the Series 9 and Ultra 2. This story will be updated as we receive more information. 

When will Apple stop selling the Apple Watch Series 9 and Ultra 2?

Apple will stop selling the Series 9 and Ultra 2 online at noon PT (3 p.m. ET) on Dec. 21, according to the company. It said the last time for the pickup and delivery of online orders, as well as in-store sales, will be the end of the day on Dec. 24.

Can I still buy the Apple Watch Series 9 and Ultra 2 from other retailers?

The order affects sales of the Apple Watch Series 9 and Ultra 2 through Apple specifically. But 9to5Mac points out that the order prohibits Apple from importing these watches and selling them to resellers, which means they may only be available through other retailers for a limited time. 

However, the order only applies to sales in the US, meaning you should still be able to purchase the Series 9 and Ultra 2 abroad. 

Best Buy told CNET it will continue selling the Apple Watch Series 9 and Ultra 2 in the US after Dec. 25 even if the order stands. Amazon, Walmart and Target have not yet responded to CNET's question about whether the affected watches will continue to be sold. Walmart, however, has said it doesn't plan to stop selling the Series 9 and Ultra 2, according to Bloomberg.

Which Apple Watch models are affected?

The Apple Watch Series 9 and Apple Watch Ultra 2 are the only models affected. Since the legal dispute involves the blood oxygen sensing tech used in the Apple Watch, the Apple Watch SE will continue to be sold as usual. The Apple Watch SE is the lower-end model in Apple's lineup, meaning it's missing some health tracking features like blood oxygen sensing and the ability to take an ECG.

Current Apple Watches with blood oxygen monitoring, which includes any non-SE models starting with the Series 6, also won't be affected.

What is Masimo and why is Apple pausing sales?

Masimo is a medical technology company that creates professional and consumer health products, including a smartwatch called the Masimo W1. The sales pause is the latest development in an ongoing legal dispute between Apple and Masimo, in which the latter accused Apple of infringing on its pulse oximeter patents. 

What happens next?

The presidential review period ends on Dec. 25, so we're expecting to learn more about whether the import ban will stand after that deadline. Apple also plans to appeal the ITC's decision to the federal circuit, the company said. 

It's rare for an order like this to be vetoed, said Rochelle Dreyfuss, professor of law emerita at the New York University School of Law. But it's happened before, specifically in 2013 when the Obama administration vetoed a ban that would have blocked the sale of certain older iPhone and iPad models in the US after the ITC found that Apple had infringed on Samsung patents.

The Apple Watch is a health product, which could work in Apple's favor when it comes to the presidential review process, Dreyfuss said. But there are also plenty of other products that offer blood oxygen monitoring, which is the specific function at the heart of the legal dispute.

"Are there other industries that provide exactly the same service? So can Americans actually get that product? That's something that the industry has already decided against Apple. So this would be the president sort of interfering with that decision," Dreyfuss added, referring to if the Biden administration were to veto the ITC decision.

Apple is said to be developing a software change that alters how the watches monitor and present blood oxygen levels as a workaround, according to Bloomberg. Apple did not immediately respond to CNET's request for comment regarding the supposed change.

If I can't buy an Apple Watch Series 9 or Ultra 2, what are my alternatives?

It's worth waiting to see what happens after the presidential review process before making any decisions. Those with an iPhone who just want a smartwatch for tracking activity, workouts and sleep should consider the $249 Apple Watch SE. While that watch lacks ECG and blood oxygen monitoring, it can still provide notifications for high and low heart rates and irregular heart rhythms. 

The Apple Watch SE is the best choice for those who are most comfortable in Apple's ecosystem, but there are also other options that work across iPhone and Android, like the Fitbit Versa 4 and Garmin Venu 3.

Those who are looking to monitor blood oxygen levels from home specifically should consider buying a standalone pulse oximeter, said Jennifer Schrack, professor in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health. 

"Consumer wearables are a great supplemental way for people stay informed about their health, but they are subject to error," Schrack said over email. "It is important to remember that they are measuring blood oxygen using PPG sensors, which can be affected by things like skin tone."

But again, if your heart is set on the Series 9 or Ultra 2, and you aren't in a position to buy one right now, it's worth waiting to see whether the ITC's order stands before making a decision.