Anything, be it a physical ship or an electromagnetic signal - radio, arriving faster than light would break causality, as it would be travelling back in time.

Someone that explains this quite well is Prof David Kipping. Watch this video: https://youtu.be/an0M-wcHw5A

It took me a couple of tries to understand the setup of the charts, but after that, it is obvious there would be a problem. Give it a try. You won't be dissapointed.