If you have an Apple Watch on your Christmas list, you'd better hope Santa's already done his shopping. Because starting later this week, you won't be able to purchase the Apple Watch Ultra 2 or the Apple Watch Series 9 -- at least not directly from Apple.

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Both watches will disappear from Apple's website at 3 p.m. EST on Thursday and from Apple stores after December 24. The halt in sales is a result of an October ruling from the International Trade Commission (ITC) regarding the Apple Watch's blood oxygen sensor.

In short, Apple is being accused of infringing on a patent from medical technology company Masimo. The two companies met a decade ago to discuss potential collaboration, but Masimo now claims that that meeting was just to find out the features -- and staff -- Apple wanted to take. 

Ahead of the initial Apple Watch launch, Apple did indeed hire several Masimo employees. Later, the company would introduce the blood oxygen sensor that's now at the center of the controversy -- technology that Masimo had been working on. 

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Masimo would end up suing Apple in 2020, asking for an injunction to stop the sale of all Apple Watch devices with the offending technology. A judge ruled that Apple was in violation, that ruling went to the ITC, and it has been in the hands of President Biden for a 60-day review. President Biden could veto the ruling, but given the review period ends on Christmas Day, and that hasn't happened yet, Apple is preparing to comply with the ban. 

Apple denies any wrongdoing and has stated it "strongly disagrees with the order and is pursuing a range of legal and technical options to ensure that Apple Watch is available to customers."

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There are two major things to note with this case. First, the ban only applies to Apple selling the devices, meaning the products are still going to be available from other retailers like Best Buy and Amazon. And second, the ban only applies to devices that offer blood oxygen monitoring, meaning models like the Apple Watch SE are still available. 

It's also important to note that the ban also stops Apple fromimportingthe watches, too, meaning Apple can't send the devices to retailers that are now selling them. So if the ruling is upheld (which seems to be the case), there will likely be a shortage of watches in stores. 

Any watches already sold with the blood oxygen sensor aren't affected.

Apple

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• The best VPNs for iPhone and iPad you can buy