Official Canon statement: "Shenzhen Jueying Technology Co. Ltd. manufactures autofocus lenses for the Canon RF mount under the brand name "Viltrox". Canon believes that these products infringe their patent and design rights and has therefore requested the company to stop all activities that infringe Canon's intellectual property rights."
Official Tamron statement: "[the 70-300mm f/4.5-6.3] is developed, manufactured and sold...under the license agreement with Sony Corporation...[and] under the license agreement with Nikon Corporation."
So, Big Red is threatening the third party lens makers with legal action, while Big Orange and Yellow are cooperating with third party lens makers. Of course, Tamron lenses in the Nikon Z-mount are US$200-300 more expensive than the same lens in the Sony FE mount, so the customer is still getting the shaft, but at least they can get the shaft ;~).
Remember, you're buying SYSTEMS cameras, so maybe you ought to pay attention to just how extensive that system is likely to get, and whether those options are coming from one or many companies.
Sony did the right thing with their mirrorless efforts. They've been licensing the specifications for the E/FE mount since the beginning. Nikon appears to now be doing the same thing, as we already have confirmed licenses from Cosina (Voigtlander) and Tamron, and Nikon executives have demonstrated Viltrox lenses in the Z mount.
Put another way, Canon seems to be currently headed towards a closed, proprietary approach, while its camera competitors (including Fujifilm, Leica, Nikon, Olympus, Panasonic, Sigma, and Sony) are all taking a more open, expand-the-ecosystem approach.
When a large, mature company locks its kimono shut, I read that as a sign of weakness. They're not sure that they can win by simply making better products.
Canon's "no you can't do that" legal team threat is classic protectionism. Technically, reverse engineering a "patented" protocol using a clean room technique is legal throughout most of the world. But by threatening to tie the smaller company up in court and exhausting them via on-going legal costs, it's essentially a clear anti-competitive practice. I had this happen to one of my companies once. Only when the case got to the discovery process, the Giant Corporation found out that we Small Fry had dotted all our i's and crossed all our t's in terms of reverse engineering. Giant concluded they were going to lose the case, big time, which would have had a more profound impact on them than just paying us off to settle.
Canon's sent out the cease and desist letters. It appears that the first two recipients have decided the cost of legal action isn't worth the possible sales profit. What we have happening now is what is known in legal parlance as the Chilling Effect.
The problem is that Canon's doing this at exactly the wrong time in camera history, and the Chilling Effect will be on RF mount camera sales. Talk about own goal. Most people buying cameras today already have cameras and know the photography industry pretty well; they have an expectation of lens choice. With virtually every photography Web site now writing about Canon's threat to third party lens makers, all the remaining potential buyers in the market are going to have to think about what that might mean to them. Will Canon give in and license the RF mount to Sigma and Tamron? Will Sigma and Tamron move forward without Canon's permission? Both of those companies make a ton of interesting lenses that Canon doesn't, increasing the buying options for a camera user.
Sony FE mount has the head start. Both Sigma and Tamron have a substantial number of excellent and interesting lenses for the FE mount that aren't available elsewhere. Tamron has started working with Nikon in the Z mount, so it's likely that we'll see a steady stream of non-Nikkors that are interesting, as well. Canon RF mount? Sorry, mount not open to the public...
Yeah, that's going to work out well for Canon, isn't it?
