Is Warner Bros blocking Universal Orlando from using Fantastic Worlds as its fourth park name?

It all comes down to what the contracts say. I doubt WB has any ground to refuse Universal the right to use "Fantastic" in the name of their new theme park. The saber rattling here sounds more like a trial balloon than anything else, and I'm not even sure why WB would be concerned since the connection of the new park to Fantastic Beasts can only serve to help the franchise.

As far as using Fantastic Beasts in the new park, it's unclear what Universal's HP license includes. Fantastic Beasts is being written exclusively for the screen by Rowling, so one would surmise that what she's writing for the movies are solely the property of WB. However, Universal is very clever with their contracts (see Marvel Super Hero Island), so I wouldn't put it past them to have rights to anything remotely related to Harry Potter, which would include Newt Scamandar's journeys.

I'm not sure what other WB properties you're talking about, but HP/FB are the only ones currently used by Universal, and there have been no other rumors of Universal purchasing any other licenses. In fact, it appears that the only other outside license that they will exploit anytime soon will be the Nintendo license with all of the other rumored attractions centered around Dreamworks, Illumination, and Universal-proper IPs. Now if you're talking about Kong/Godzilla, or LOTR, I don't think you understand how licensing works. Universal already owns rights to Kong (but not Godzilla), and would need to negotiate with the Tolkein family in order to put LOTR in the theme parks before even approaching WB/New Line regarding using Peter Jackson's vision of Middle Earth.

This noise is just typical for the entertainment industry as a scare tactic where nothing much will come to fruition. Universal likely has a Plan B if necessary, but I doubt WB really has a leg to stand on here, and is just leveraging this name overlap in an attempt to get a revised WWoHP licensing deal (i.e. bigger cut of the $$$).

I’d be surprised if they do. I don’t think Warner’s are too interested in entering the US Theme Park space again, themed attractions ala the studio tour maybe, but a whole park when much of their IP is already licensed out (Universal, Six Flags, etc) strikes me as a “brave and courageous” idea.

Now maybe using the trademark as a part of a negotiating strategy on something else I can buy.

RM writes "...Universal is very clever with their contracts (see Marvel Super Hero Island) ..."

I Respond: If it had been "clever" they would have negotiated a contract that would have given them the rights across the continental United States and the "Amazing Adventures of Spider Man" would be operating tonight at USH.

If the contract wasn't so "clever", then why is Disney being so hesitant about the application of an IP they own in California? They aren't even using the Marvel name in California, even for a land in development that is clearly grounded in the MCU. That contract must be clever enough to give them pause.

""Amazing Adventures of Spider Man" would be operating tonight at USH."

According to some here on this website, it is - Transformers.

RM writes: "That contract must be clever enough to give them pause."

I Respond: Or there's another reason that has nothing to do with the UO IOA licensing agreement.

Universal HAD the rights to build a Spider-Man attraction in Hollywood. But it didn't do that by the deadline specified in the original Marvel contract, so its rights to use Marvel in the western U.S. lapsed.

This was at the end of the Vivendi era at Universal, before Comcast bought the company, Potter blew up in Orlando, and Universal found itself swimming in cash to build lots of new stuff. If the original Marvel contract had given Universal five more years to build in Hollywood, it probably goes ahead with a Spider-Man ride, Disney is blocked from using Marvel at Disneyland... and possibly that dissuades Disney from buying Marvel at all. Who knows?