system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it legal for Hershey's to block Cadbury's chocolate from entering the US?

Edit: Some really good responses, thanks folks. For the record I'm a Brit and feel lucky that these shenanigans don't affect my chocolate stash. I feel for you America.
gpt
It's not Hershey's blocking Cadbury's.  It's Cadbury's blocking Cadbury's because they've sold the rights to Hershey. 

Cadbury's signed a contract with Hershey's stating that Hershey's would manufacture chocolate in the US and sell it in the US under the Cadbury's name.  Hersheys paid Cadbury's a sum of money for this privilege.  In return Hershey's gets to use the Cadbury's name and advertizing.  In addition Cadbury's agrees not to sell it's own chocolate within the United States.

The problem here is that people are importing Cadbury's from the UK and selling it in the US.  If Cadbury's does not take steps to prevent this then Hershey's could sue them for breaching the contract mentioned above.  Since Cadbury's actually likes that contract (because of all the money Hershey's pays them) then don't like these chocolate importers.  So they attempt to block it.

It's not Hershey's doing the blocking.  It's Cadbury honoring the commitment they made when they signed that contract.