Serious question if there's anyone with an appropriate background in the relevant law: how does this play with net neutrality and FCC regulation if the ISP is b

Serious question if there's anyone with an appropriate background in the relevant law: how does this play with net neutrality and FCC regulation if the ISP is blocking Facebook and Twitter but not their competitors? It's not a free speech issue, but are there any fair dealing and business regulations that would come into play? In Canada, where ISPs are usually treated like public utilities, I believe that this would not be permitted, but I don't know the current state of Net neutrality in the US.